From 6b484b48f8f79d53467cdafaaef834413ca7d9c2 Mon Sep 17 00:00:00 2001
From: Dave Townsend <dtownsend@oxymoronical.com>
Date: Tue, 19 Mar 2024 14:59:21 +0000
Subject: [PATCH] Bug 1864896: Autofix unused function arguments (toolkit).
 r=mconley,translations-reviewers,omc-reviewers,aminomancer

Differential Revision: https://phabricator.services.mozilla.com/D203002
---
 toolkit/actors/AutoplayChild.sys.mjs          |   2 +-
 toolkit/actors/AutoplayParent.sys.mjs         |   2 +-
 toolkit/actors/ControllersParent.sys.mjs      |   2 +-
 toolkit/actors/NetErrorParent.sys.mjs         |   4 +-
 toolkit/actors/PictureInPictureChild.sys.mjs  |  18 ++--
 toolkit/actors/PrintingChild.sys.mjs          |   2 +-
 toolkit/actors/SelectChild.sys.mjs            |   2 +-
 toolkit/actors/ViewSourcePageChild.sys.mjs    |   2 +-
 .../aboutconfig/content/aboutconfig.js        |   2 +-
 .../aboutmemory/content/aboutMemory.js        |   4 +-
 .../aboutmemory/tests/test_aboutmemory.xhtml  |  10 +-
 .../aboutmemory/tests/test_aboutmemory2.xhtml |   2 +-
 .../aboutmemory/tests/test_aboutmemory3.xhtml |   2 +-
 .../aboutmemory/tests/test_aboutmemory4.xhtml |   2 +-
 .../aboutmemory/tests/test_aboutmemory7.xhtml |   2 +-
 .../tests/test_memoryReporters.xhtml          |  10 +-
 .../tests/test_memoryReporters2.xhtml         |   2 +-
 .../tests/xpcshell/test_gpuprocess.js         |   9 +-
 .../aboutprocesses/content/aboutProcesses.js  |   4 +-
 .../tests/browser/browser_aboutthirdparty.js  |   2 +-
 .../aboutwebauthn/content/aboutWebauthn.js    |   4 +-
 .../browser_aboutwebauthn_credentials.js      |   2 +-
 .../browser/browser_aboutwindowsmessages.js   |   2 +-
 .../test/test_alerts_requireinteraction.html  |   4 +-
 .../alerts/test/test_invalid_utf16.html       |   2 +-
 .../alerts/test/test_multiple_alerts.html     |   2 +-
 .../alerts/test/test_principal.html           |   2 +-
 .../tests/unit/head_autocomplete.js           |   8 +-
 .../autocomplete/tests/unit/test_378079.js    |   8 +-
 .../autocomplete/tests/unit/test_393191.js    |   8 +-
 .../autocomplete/tests/unit/test_440866.js    |   8 +-
 .../tests/unit/test_autocomplete_multiple.js  |   8 +-
 .../unit/test_autocomplete_userContextId.js   |   7 +-
 .../tests/unit/test_previousResult.js         |   8 +-
 .../tests/unit/test_stopSearch.js             |   2 +-
 .../BHRTelemetryService.sys.mjs               |   2 +-
 .../BackgroundTask_message.sys.mjs            |   5 +-
 .../BackgroundTasksManager.sys.mjs            |   2 +-
 .../BackgroundTasksUtils.sys.mjs              |   2 +-
 .../tests/BackgroundTask_jsdebugger.sys.mjs   |   2 +-
 ...ackgroundTask_shouldprocessupdates.sys.mjs |   2 +-
 .../tests/BackgroundTask_targeting.sys.mjs    |   2 +-
 .../captivedetect/CaptiveDetect.sys.mjs       |   9 +-
 .../captivedetect/test/unit/test_abort.js     |   4 +-
 .../test/unit/test_abort_during_user_login.js |   2 +-
 .../test/unit/test_abort_ongoing_request.js   |   4 +-
 .../test/unit/test_abort_pending_request.js   |   4 +-
 .../test/unit/test_captive_portal_found.js    |   4 +-
 .../unit/test_captive_portal_found_303.js     |   4 +-
 .../unit/test_captive_portal_not_found.js     |   2 +-
 .../unit/test_captive_portal_not_found_404.js |   2 +-
 .../test/unit/test_multiple_requests.js       |   4 +-
 .../certviewer/content/certviewer.mjs         |   4 +-
 .../browser/browser_openTabAndSendCertInfo.js |   2 +-
 .../certviewer/tests/browser/head.js          |   2 +-
 .../cleardata/ClearDataService.sys.mjs        |  42 ++++----
 .../cleardata/SiteDataTestUtils.sys.mjs       |   8 +-
 .../cleardata/tests/unit/test_permissions.js  |   4 +-
 .../tests/unit/test_storage_permission.js     |   8 +-
 .../contentprefs/ContentPrefService2.sys.mjs  |   7 +-
 .../ContentPrefServiceParent.sys.mjs          |   2 +-
 .../browser/browser_remoteContentPrefs.js     |   4 +-
 .../contentprefs/tests/unit_cps2/head.js      |   4 +-
 .../unit_cps2/test_migrationToSchema4.js      |   2 +-
 .../ContextualIdentityService.sys.mjs         |   2 +-
 .../components/crashes/CrashService.sys.mjs   |   4 +-
 .../tests/xpcshell/test_crash_manager.js      |   2 +-
 .../tests/xpcshell/test_crash_service.js      |   2 +-
 .../tests/xpcshell/test_crash_store.js        |   2 +-
 .../crashmonitor/CrashMonitor.sys.mjs         |   2 +-
 .../crashmonitor/nsCrashMonitor.sys.mjs       |   2 +-
 .../chrome/xpcshellTestHarnessAdaptor.js      |   2 +-
 .../ctypes/tests/unit/test_jsctypes.js        |   2 +-
 .../EnterprisePoliciesParent.sys.mjs          |   2 +-
 .../browser_policies_enterprise_only.js       |   4 +-
 .../test/unit/head_forgetaboutsite.js         |   2 +-
 toolkit/components/gfx/SanityTest.sys.mjs     |   2 +-
 .../components/gfx/content/gfxFrameScript.js  |   2 +-
 .../tests/browser/browser_exception.js        |   2 +-
 .../test/unit/test_mediasniffer.js            |   4 +-
 .../test/unit/test_mediasniffer_ext.js        |   4 +-
 .../lib/SpecialMessageActions.sys.mjs         |   2 +-
 .../browser_sma_open_protection_panel.js      |   2 +-
 .../browser/browser_sma_pin_current_tab.js    |   2 +-
 .../ml/actors/MLEngineParent.sys.mjs          |   2 +-
 .../components/pdfjs/content/PdfJs.sys.mjs    |   2 +-
 .../pdfjs/content/PdfJsNetwork.sys.mjs        |   4 +-
 .../pdfjs/content/PdfStreamConverter.sys.mjs  |   8 +-
 .../pdfjs/content/PdfjsParent.sys.mjs         |   2 +-
 .../pdfjs/test/browser_pdfjs_find.js          |   2 +-
 .../test/browser_pdfjs_force_opening_files.js |   4 +-
 .../pdfjs/test/browser_pdfjs_fullscreen.js    |   2 +-
 .../pdfjs/test/browser_pdfjs_navigation.js    |   2 +-
 .../pdfjs/test/browser_pdfjs_octet_stream.js  |   2 +-
 .../pdfjs/test/browser_pdfjs_savedialog.js    |   2 +-
 toolkit/components/printing/content/print.js  |  18 ++--
 .../tests/browser_preview_navigation.js       |   2 +-
 .../tests/file_window_print_reentrant.html    |   2 +-
 toolkit/components/printing/tests/head.js     |   6 +-
 .../MainProcessSingleton.sys.mjs              |   2 +-
 .../browser/browser_test_powerMetrics.js      |  14 +--
 .../tests/browser/browser_test_procinfo.js    |   2 +-
 .../tests/xpcshell/data/worker.js             |   2 +-
 .../tests/xpcshell/data/worker.mjs            |   2 +-
 .../prompts/src/CommonDialog.sys.mjs          |   2 +-
 .../components/prompts/src/Prompter.sys.mjs   |  22 +---
 .../components/prompts/test/prompt_common.js  |   4 +-
 .../prompts/test/test_bug619644.html          |   2 +-
 toolkit/components/reader/AboutReader.sys.mjs |   2 +-
 toolkit/components/reader/ReaderMode.sys.mjs  |   2 +-
 .../reader/test/browser_readerMode.js         |   2 +-
 .../test/browser_readerMode_hidden_nodes.js   |   2 +-
 .../tests/browser/browser_documentChannel.js  |   4 +-
 .../browser_httpCrossOriginOpenerPolicy.js    |   2 +-
 .../ReportBrokenSiteChild.sys.mjs             |   2 +-
 .../test/unit/test_app_rep.js                 |   2 +-
 .../test/unit/test_app_rep_maclinux.js        |   2 +-
 .../test/unit/test_app_rep_windows.js         |   2 +-
 .../resistfingerprinting/RFPHelper.sys.mjs    |   2 +-
 ...rowser_fpiServiceWorkers_fingerprinting.js |   2 +-
 ..._serviceWorker_fingerprinting_webcompat.js |   4 +-
 .../tests/browser/head.js                     |   2 +-
 .../shopping/content/ShoppingProduct.mjs      |   2 +-
 .../test/browser/browser_shopping_ads_test.js |   2 +-
 .../browser_shopping_sidebar_messages.js      |   8 +-
 .../components/shopping/test/browser/head.js  |   4 +-
 .../tests/browser/browser_bug511456.js        |   2 +-
 .../tests/browser/browser_bug537449.js        |   2 +-
 .../TaskSchedulerMacOSImpl.sys.mjs            |   4 +-
 .../terminator/TerminatorTelemetry.sys.mjs    |   2 +-
 .../thumbnails/BackgroundPageThumbs.sys.mjs   |   4 +-
 .../components/thumbnails/PageThumbs.sys.mjs  |   4 +-
 .../browser_thumbnails_bg_captureIfMissing.js |   2 +-
 .../test/browser_thumbnails_bug727765.js      |   2 +-
 .../test/browser_thumbnails_bug818225.js      |   2 +-
 .../test/browser_thumbnails_redirect.js       |   4 +-
 .../test/browser_thumbnails_storage.js        |   2 +-
 .../test/browser_thumbnails_update.js         |   8 +-
 .../timermanager/UpdateTimerManager.sys.mjs   |   2 +-
 .../tests/unit/consumerNotifications.js       |  20 ++--
 .../tooltiptext/tests/browser_bug581947.js    |   2 +-
 .../browser_about_translations_dropdowns.js   |   2 +-
 .../translations/tests/browser/shared-head.js |   2 +-
 .../utils/ClientEnvironment.sys.mjs           |   2 +-
 .../components/utils/SimpleServices.sys.mjs   |   2 +-
 .../test/browser/browser_contextmenu.js       |   2 +-
 .../browser/browser_viewsource_newwindow.js   |   4 +-
 .../windowcreator/test/test_bug449141.html    |   2 +-
 .../browser_new_content_window_chromeflags.js |   8 +-
 .../test/browser_new_remote_window_flags.js   |   2 +-
 .../test/browser_new_sized_window.js          |   2 +-
 .../test/browser_non_popup_from_popup.js      |   2 +-
 toolkit/components/windowwatcher/test/head.js |   4 +-
 .../workerloader/tests/worker_test_loading.js |   2 +-
 toolkit/components/xulstore/XULStore.sys.mjs  |   2 +-
 toolkit/content/aboutLogging.js               |   4 +-
 toolkit/content/aboutNetError.mjs             |   8 +-
 toolkit/content/aboutProfiles.js              |   2 +-
 toolkit/content/aboutSupport.js               |  32 +++---
 toolkit/content/aboutTelemetry.js             |   6 +-
 toolkit/content/aboutUrlClassifier.js         |   2 +-
 toolkit/content/aboutwebrtc/aboutWebrtc.mjs   |   8 +-
 toolkit/content/aboutwebrtc/graph.mjs         |   8 +-
 toolkit/content/contentAreaUtils.js           |  10 +-
 .../tests/browser/browser_about_logging.js    |   4 +-
 .../tests/browser/browser_bug982298.js        |   2 +-
 .../browser/browser_f7_caret_browsing.js      |   2 +-
 .../tests/browser/browser_isSynthetic.js      |   2 +-
 .../browser_media_wakelock_webaudio.js        |   1 -
 .../browser_save_folder_standalone_image.js   |   2 +-
 .../browser/browser_save_resend_postdata.js   |   2 +-
 .../tests/browser/common/mockTransfer.js      |   3 +-
 .../content/tests/browser/datetime/head.js    |   2 +-
 toolkit/content/tests/browser/head.js         |   2 +-
 .../tests/chrome/bug263683_window.xhtml       |   2 +-
 .../tests/chrome/bug366992_window.xhtml       |   2 +-
 .../chrome/file_editor_with_autocomplete.js   |  60 +++++------
 toolkit/content/tests/chrome/popup_trigger.js | 100 +++++++++---------
 .../tests/chrome/test_arrowpanel.xhtml        |   2 +-
 .../tests/chrome/test_menuitem_blink.xhtml    |   2 +-
 .../tests/chrome/test_menulist_in_popup.xhtml |   2 +-
 .../tests/chrome/test_notificationbox.xhtml   |  18 ++--
 .../tests/chrome/test_popup_keys.xhtml        |   2 +-
 .../chrome/test_popup_moveToAnchor.xhtml      |   2 +-
 .../content/tests/chrome/test_tree_view.xhtml |  26 ++---
 .../chrome/window_cursorsnap_dialog.xhtml     |   2 +-
 .../chrome/window_maximized_persist.xhtml     |   2 +-
 ...w_maximized_persist_with_no_titlebar.xhtml |   2 +-
 .../chrome/window_popup_anchoratrect.xhtml    |   2 +-
 toolkit/content/tests/widgets/head.js         |   2 +-
 .../content/tests/widgets/test_moz_card.html  |   2 +-
 .../tests/widgets/test_popupreflows.xhtml     |   4 +-
 .../tests/widgets/test_videocontrols.html     |   2 +-
 .../widgets/test_videocontrols_audio.html     |   2 +-
 .../test_videocontrols_jsdisabled.html        |   2 +-
 .../test_videocontrols_onclickplay.html       |   2 +-
 toolkit/content/tests/widgets/tree_shared.js  |  14 +--
 .../widgets/videocontrols_direction_test.js   |   2 +-
 .../tests/widgets/window_menubar.xhtml        |   8 +-
 toolkit/crashreporter/CrashSubmit.sys.mjs     |   2 +-
 .../test/unit/test_crash_stack_overflow.js    |   2 +-
 .../test/unit/test_crashreporter_appmem.js    |   2 +-
 .../test/unit/test_event_files.js             |   2 +-
 .../unit/test_override_exception_handler.js   |   2 +-
 .../test/unit_ipc/test_content_memory_list.js |   2 +-
 toolkit/modules/AppMenuNotifications.sys.mjs  |   2 +-
 toolkit/modules/AsanReporter.sys.mjs          |   2 +-
 toolkit/modules/AsyncPrefs.sys.mjs            |   2 +-
 toolkit/modules/FindBarContent.sys.mjs        |   4 +-
 toolkit/modules/Finder.sys.mjs                |   2 +-
 toolkit/modules/FinderHighlighter.sys.mjs     |  10 +-
 toolkit/modules/FinderParent.sys.mjs          |   2 +-
 toolkit/modules/GMPInstallManager.sys.mjs     |   2 +-
 toolkit/modules/HiddenFrame.sys.mjs           |   2 +-
 .../modules/LightweightThemeConsumer.sys.mjs  |   8 +-
 toolkit/modules/NewTabUtils.sys.mjs           |   8 +-
 toolkit/modules/PopupNotifications.sys.mjs    |   4 +-
 toolkit/modules/Region.sys.mjs                |   2 +-
 toolkit/modules/UpdateUtils.sys.mjs           |   2 +-
 .../modules/tests/browser/browser_Finder.js   |   4 +-
 .../browser/browser_FinderHighlighter.js      |   2 +-
 .../tests/browser/browser_Troubleshoot.js     |   6 +-
 .../tests/browser/browser_web_channel.js      |  42 ++++----
 toolkit/modules/tests/browser/head.js         |   2 +-
 .../tests/modules/MockDocument.sys.mjs        |   2 +-
 .../tests/xpcshell/test_DeferredTask.js       |   2 +-
 .../tests/xpcshell/test_FinderIterator.js     |  28 ++---
 .../tests/xpcshell/test_GMPInstallManager.js  |  13 ++-
 .../tests/xpcshell/test_Integration.js        |   2 +-
 toolkit/modules/tests/xpcshell/test_sqlite.js |  37 +++----
 .../tests/xpcshell/test_web_channel.js        |   4 +-
 .../tests/xpcshell/test_web_channel_broker.js |   2 +-
 .../test/browser_checkdllblockliststate.js    |   2 +-
 toolkit/xre/test/test_launch_without_hang.js  |   6 +-
 .../win/mochitest/browser_env_path_long.js    |   2 +-
 235 files changed, 570 insertions(+), 631 deletions(-)

diff --git a/toolkit/actors/AutoplayChild.sys.mjs b/toolkit/actors/AutoplayChild.sys.mjs
index 87fa966cb1e3..42bff87ea141 100644
--- a/toolkit/actors/AutoplayChild.sys.mjs
+++ b/toolkit/actors/AutoplayChild.sys.mjs
@@ -4,7 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 export class AutoplayChild extends JSWindowActorChild {
-  handleEvent(event) {
+  handleEvent() {
     this.sendAsyncMessage("GloballyAutoplayBlocked", {});
   }
 }
diff --git a/toolkit/actors/AutoplayParent.sys.mjs b/toolkit/actors/AutoplayParent.sys.mjs
index 3e9f807b3a47..7b33c49c7fb2 100644
--- a/toolkit/actors/AutoplayParent.sys.mjs
+++ b/toolkit/actors/AutoplayParent.sys.mjs
@@ -4,7 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 export class AutoplayParent extends JSWindowActorParent {
-  receiveMessage(aMessage) {
+  receiveMessage() {
     let topBrowsingContext = this.manager.browsingContext.top;
     let browser = topBrowsingContext.embedderElement;
     let document = browser.ownerDocument;
diff --git a/toolkit/actors/ControllersParent.sys.mjs b/toolkit/actors/ControllersParent.sys.mjs
index 05ea16611259..8461d76ba27c 100644
--- a/toolkit/actors/ControllersParent.sys.mjs
+++ b/toolkit/actors/ControllersParent.sys.mjs
@@ -47,7 +47,7 @@ export class ControllersParent extends JSWindowActorParent {
     this.sendAsyncMessage("ControllerCommands:Do", aCommand);
   }
 
-  getCommandStateWithParams(aCommand, aCommandParams) {
+  getCommandStateWithParams() {
     throw Components.Exception("Not implemented", Cr.NS_ERROR_NOT_IMPLEMENTED);
   }
 
diff --git a/toolkit/actors/NetErrorParent.sys.mjs b/toolkit/actors/NetErrorParent.sys.mjs
index ac0dbf49a07c..071529976a54 100644
--- a/toolkit/actors/NetErrorParent.sys.mjs
+++ b/toolkit/actors/NetErrorParent.sys.mjs
@@ -33,7 +33,7 @@ class CaptivePortalObserver {
     Services.obs.removeObserver(this, "captive-portal-login-success");
   }
 
-  observe(aSubject, aTopic, aData) {
+  observe(aSubject, aTopic) {
     switch (aTopic) {
       case "captive-portal-login-abort":
       case "captive-portal-login-success":
@@ -172,7 +172,7 @@ export class NetErrorParent extends JSWindowActorParent {
     request.channel.loadFlags |= Ci.nsIRequest.LOAD_BYPASS_CACHE;
     request.channel.loadFlags |= Ci.nsIRequest.INHIBIT_CACHING;
 
-    request.addEventListener("error", event => {
+    request.addEventListener("error", () => {
       // Make sure the user is still on the cert error page.
       if (!browser.documentURI.spec.startsWith("about:certerror")) {
         return;
diff --git a/toolkit/actors/PictureInPictureChild.sys.mjs b/toolkit/actors/PictureInPictureChild.sys.mjs
index 2a415df32db6..bffcb55e6d67 100644
--- a/toolkit/actors/PictureInPictureChild.sys.mjs
+++ b/toolkit/actors/PictureInPictureChild.sys.mjs
@@ -947,11 +947,8 @@ export class PictureInPictureToggleChild extends JSWindowActorChild {
    * tear out or in. If we happened to be tracking videos before the tear
    * occurred, we re-add the mouse event listeners so that they're attached to
    * the right WindowRoot.
-   *
-   * @param {Event} event The pageshow event fired when completing a tab tear
-   * out or in.
    */
-  onPageShow(event) {
+  onPageShow() {
     let state = this.docState;
     if (state.isTrackingVideos) {
       this.addMouseButtonListeners();
@@ -963,11 +960,8 @@ export class PictureInPictureToggleChild extends JSWindowActorChild {
    * tear out or in. If we happened to be tracking videos before the tear
    * occurred, we remove the mouse event listeners. We'll re-add them when the
    * pageshow event fires.
-   *
-   * @param {Event} event The pagehide event fired when starting a tab tear
-   * out or in.
    */
-  onPageHide(event) {
+  onPageHide() {
     let state = this.docState;
     if (state.isTrackingVideos) {
       this.removeMouseButtonListeners();
@@ -1049,7 +1043,7 @@ export class PictureInPictureToggleChild extends JSWindowActorChild {
     }
   }
 
-  startPictureInPicture(event, video, toggle) {
+  startPictureInPicture(event, video) {
     Services.telemetry.keyedScalarAdd(
       "pictureinpicture.opened_method",
       "toggle",
@@ -2445,7 +2439,7 @@ export class PictureInPictureChild extends JSWindowActorChild {
     }
   }
 
-  onCueChange(e) {
+  onCueChange() {
     if (!lazy.DISPLAY_TEXT_TRACKS_PREF) {
       this.updateWebVTTTextTracksDisplay(null);
     } else {
@@ -3110,10 +3104,10 @@ class PictureInPictureChildVideoWrapper {
    * a cue change is triggered {@see updatePiPTextTracks()}.
    * @param {HTMLVideoElement} video
    *  The originating video source element
-   * @param {Function} callback
+   * @param {Function} _callback
    *  The callback function to be executed when cue changes are detected
    */
-  setCaptionContainerObserver(video, callback) {
+  setCaptionContainerObserver(video, _callback) {
     return this.#callWrapperMethod({
       name: "setCaptionContainerObserver",
       args: [
diff --git a/toolkit/actors/PrintingChild.sys.mjs b/toolkit/actors/PrintingChild.sys.mjs
index 4fca3ab4038b..182784cfe74b 100644
--- a/toolkit/actors/PrintingChild.sys.mjs
+++ b/toolkit/actors/PrintingChild.sys.mjs
@@ -94,7 +94,7 @@ export class PrintingChild extends JSWindowActorChild {
       // will wait for MozAfterPaint event to be fired.
       let actor = thisWindow.windowGlobalChild.getActor("Printing");
       let webProgressListener = {
-        onStateChange(webProgress, req, flags, status) {
+        onStateChange(webProgress, req, flags) {
           if (flags & Ci.nsIWebProgressListener.STATE_STOP) {
             webProgress.removeProgressListener(webProgressListener);
             let domUtils = contentWindow.windowUtils;
diff --git a/toolkit/actors/SelectChild.sys.mjs b/toolkit/actors/SelectChild.sys.mjs
index 1bc80001ae13..9901f7264840 100644
--- a/toolkit/actors/SelectChild.sys.mjs
+++ b/toolkit/actors/SelectChild.sys.mjs
@@ -70,7 +70,7 @@ SelectContentHelper.prototype = {
       mozSystemGroup: true,
     });
     let MutationObserver = this.element.ownerGlobal.MutationObserver;
-    this.mut = new MutationObserver(mutations => {
+    this.mut = new MutationObserver(() => {
       // Something changed the <select> while it was open, so
       // we'll poke a DeferredTask to update the parent sometime
       // in the very near future.
diff --git a/toolkit/actors/ViewSourcePageChild.sys.mjs b/toolkit/actors/ViewSourcePageChild.sys.mjs
index d5c2ba46cd94..ff8a0463278b 100644
--- a/toolkit/actors/ViewSourcePageChild.sys.mjs
+++ b/toolkit/actors/ViewSourcePageChild.sys.mjs
@@ -125,7 +125,7 @@ export class ViewSourcePageChild extends JSWindowActorChild {
    * @param event
    *        The pageshow event being handled.
    */
-  onPageShow(event) {
+  onPageShow() {
     // If we need to draw the selection, wait until an actual view source page
     // has loaded, instead of about:blank.
     if (
diff --git a/toolkit/components/aboutconfig/content/aboutconfig.js b/toolkit/components/aboutconfig/content/aboutconfig.js
index 5e67b764b538..ef4238975be6 100644
--- a/toolkit/components/aboutconfig/content/aboutconfig.js
+++ b/toolkit/components/aboutconfig/content/aboutconfig.js
@@ -509,7 +509,7 @@ function loadPrefs() {
     });
   });
 
-  showAll.addEventListener("click", event => {
+  showAll.addEventListener("click", () => {
     search.focus();
     search.value = "";
     gFilterPrefsTask.disarm();
diff --git a/toolkit/components/aboutmemory/content/aboutMemory.js b/toolkit/components/aboutmemory/content/aboutMemory.js
index 049818263f2a..6b6f2e637c75 100644
--- a/toolkit/components/aboutmemory/content/aboutMemory.js
+++ b/toolkit/components/aboutmemory/content/aboutMemory.js
@@ -608,7 +608,7 @@ function dumpGCLogAndCCLog(aVerbose) {
   );
   let section = appendElement(gMain, "div", "section");
 
-  function displayInfo(aGCLog, aCCLog, aIsParent) {
+  function displayInfo(aGCLog, aCCLog) {
     appendElementWithText(section, "div", "", "Saved GC log to " + aGCLog.path);
 
     let ccLogType = aVerbose ? "verbose" : "concise";
@@ -824,7 +824,7 @@ function loadMemoryReportsFromFile(aFilename, aTitleNote, aFn) {
       "uncompressed",
       {
         data: [],
-        onStartRequest(aR, aC) {},
+        onStartRequest() {},
         onDataAvailable(aR, aStream, aO, aCount) {
           let bi = new nsBinaryStream(aStream);
           this.data.push(bi.readBytes(aCount));
diff --git a/toolkit/components/aboutmemory/tests/test_aboutmemory.xhtml b/toolkit/components/aboutmemory/tests/test_aboutmemory.xhtml
index 4617a019adb2..a1a712dd0a16 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutmemory.xhtml
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory.xhtml
@@ -40,7 +40,7 @@
   const PERCENTAGE = Ci.nsIMemoryReporter.UNITS_PERCENTAGE;
 
   let fakeReporters = [
-    { collectReports(aCbObj, aClosure, aAnonymize) {
+    { collectReports(aCbObj, aClosure) {
         function f(aP, aK, aU, aA) {
           aCbObj.callback("Main Process", aP, aK, aU, aA, "Desc.", aClosure);
         }
@@ -77,7 +77,7 @@
         f("compartments/system/foo", OTHER, COUNT, 1);
       }
     },
-    { collectReports(aCbObj, aClosure, aAnonymize) {
+    { collectReports(aCbObj, aClosure) {
         function f(aP, aK, aU, aA) {
           aCbObj.callback("Main Process", aP, aK, aU, aA, "Desc.", aClosure);
         }
@@ -92,7 +92,7 @@
         f("explicit/f/g/h/j", HEAP,    BYTES,  10 * MB);
       }
     },
-    { collectReports(aCbObj, aClosure, aAnonymize) {
+    { collectReports(aCbObj, aClosure) {
         function f(aP, aK, aU, aA) {
           aCbObj.callback("Main Process", aP, aK, aU, aA, "Desc.", aClosure);
         }
@@ -103,7 +103,7 @@
         f("compartments/user/https:\\\\very-long-url.com\\very-long\\oh-so-long\\really-quite-long.html?a=2&b=3&c=4&d=5&e=abcdefghijklmnopqrstuvwxyz&f=123456789123456789123456789", OTHER, COUNT, 1);
       }
     },
-    { collectReports(aCbObj, aClosure, aAnonymize) {
+    { collectReports(aCbObj, aClosure) {
         function f(aP) {
           aCbObj.callback("Main Process", aP, OTHER, COUNT, 1, "Desc.", aClosure);
         }
@@ -121,7 +121,7 @@
   // the largest).  Processes without a |resident| memory reporter are saved
   // for the end.
   let fakeReporters2 = [
-    { collectReports(aCbObj, aClosure, aAnonymize) {
+    { collectReports(aCbObj, aClosure) {
         function f(aP1, aP2, aK, aU, aA) {
           aCbObj.callback(aP1, aP2, aK, aU, aA, "Desc.", aClosure);
         }
diff --git a/toolkit/components/aboutmemory/tests/test_aboutmemory2.xhtml b/toolkit/components/aboutmemory/tests/test_aboutmemory2.xhtml
index 28c8f7fa4f02..f5c388595925 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutmemory2.xhtml
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory2.xhtml
@@ -36,7 +36,7 @@
   let jk2Path = "explicit/j/k2";
 
   let fakeReporters = [
-    { collectReports(aCbObj, aClosure, aAnonymize) {
+    { collectReports(aCbObj, aClosure) {
         function f(aP, aK, aA) {
           aCbObj.callback("Main Process ABC", aP, aK, BYTES, aA, "Desc.", aClosure);
         }
diff --git a/toolkit/components/aboutmemory/tests/test_aboutmemory3.xhtml b/toolkit/components/aboutmemory/tests/test_aboutmemory3.xhtml
index 1391af38b716..7292cbf2526f 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutmemory3.xhtml
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory3.xhtml
@@ -31,7 +31,7 @@
   const BYTES = Ci.nsIMemoryReporter.UNITS_BYTES;
 
   let fakeReporters = [
-    { collectReports(aCbObj, aClosure, aAnonymize) {
+    { collectReports(aCbObj, aClosure) {
         function f(aP, aK, aA, aD) {
           aCbObj.callback("", aP, aK, BYTES, aA, aD, aClosure);
         }
diff --git a/toolkit/components/aboutmemory/tests/test_aboutmemory4.xhtml b/toolkit/components/aboutmemory/tests/test_aboutmemory4.xhtml
index 9d9db694f2af..1fcdb8640670 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutmemory4.xhtml
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory4.xhtml
@@ -35,7 +35,7 @@
     frame.height = 300;
     frame.src = "about:memory?file=" + makePathname(aFilename);
     document.documentElement.appendChild(frame);
-    frame.addEventListener("load", function onFrameLoad(e) {
+    frame.addEventListener("load", function onFrameLoad() {
       frame.focus();
 
       // Initialize the clipboard contents.
diff --git a/toolkit/components/aboutmemory/tests/test_aboutmemory7.xhtml b/toolkit/components/aboutmemory/tests/test_aboutmemory7.xhtml
index 28872cd516bc..a31eb6e6b4c3 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutmemory7.xhtml
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory7.xhtml
@@ -30,7 +30,7 @@
   const BYTES = Ci.nsIMemoryReporter.UNITS_BYTES;
 
   let fakeReporters = [
-    { collectReports(aCbObj, aClosure, aAnonymize) {
+    { collectReports(aCbObj, aClosure) {
         function f(aP, aK, aA) {
           aCbObj.callback("Main Process", aP, aK, BYTES, aA, "Desc.", aClosure);
         }
diff --git a/toolkit/components/aboutmemory/tests/test_memoryReporters.xhtml b/toolkit/components/aboutmemory/tests/test_memoryReporters.xhtml
index c97981258e40..bc715b677848 100644
--- a/toolkit/components/aboutmemory/tests/test_memoryReporters.xhtml
+++ b/toolkit/components/aboutmemory/tests/test_memoryReporters.xhtml
@@ -77,8 +77,7 @@
   let mySandbox = Cu.Sandbox(document.nodePrincipal,
                     { sandboxName: "this-is-a-sandbox-name" });
 
-  function handleReportNormal(aProcess, aPath, aKind, aUnits, aAmount,
-                              aDescription)
+  function handleReportNormal(aProcess, aPath, aKind, aUnits, aAmount)
   {
     if (aProcess.startsWith(`Utility `)) {
       // The Utility process that runs the ORB JavaScript validator starts on first
@@ -128,8 +127,7 @@
     }
   }
 
-  function handleReportAnonymized(aProcess, aPath, aKind, aUnits, aAmount,
-                                  aDescription)
+  function handleReportAnonymized(aProcess, aPath)
   {
     // Path might include an xmlns using http, which is safe to ignore.
     let reducedPath = aPath.replace(XUL_NS, "");
@@ -331,7 +329,7 @@
       }
     },
     // nsIMemoryReporter
-    collectReports(callback, data, anonymize) {
+    collectReports(callback, data) {
       for (let path of Object.keys(this.tests)) {
         try {
           let test = this.tests[path];
@@ -350,7 +348,7 @@
       }
     },
     // nsIHandleReportCallback
-    callback(process, path, kind, units, amount, data) {
+    callback(process, path, kind, units, amount) {
       if (path in this.tests) {
         this.seen++;
         let test = this.tests[path];
diff --git a/toolkit/components/aboutmemory/tests/test_memoryReporters2.xhtml b/toolkit/components/aboutmemory/tests/test_memoryReporters2.xhtml
index b7251c4e62a4..8dc756710958 100644
--- a/toolkit/components/aboutmemory/tests/test_memoryReporters2.xhtml
+++ b/toolkit/components/aboutmemory/tests/test_memoryReporters2.xhtml
@@ -55,7 +55,7 @@
   {
     let residents = {};
 
-    let handleReport = function(aProcess, aPath, aKind, aUnits, aAmount, aDesc) {
+    let handleReport = function(aProcess, aPath, aKind, aUnits, aAmount) {
       if (aProcess.startsWith(`Utility `)) {
         // The Utility process that runs the ORB JavaScript validator starts on first
         // idle in the parent process. This makes it notoriously hard to know _if_ it
diff --git a/toolkit/components/aboutmemory/tests/xpcshell/test_gpuprocess.js b/toolkit/components/aboutmemory/tests/xpcshell/test_gpuprocess.js
index 4a77752b1751..764f5a1302bc 100644
--- a/toolkit/components/aboutmemory/tests/xpcshell/test_gpuprocess.js
+++ b/toolkit/components/aboutmemory/tests/xpcshell/test_gpuprocess.js
@@ -17,14 +17,7 @@ function run_test() {
   };
 
   let foundGPUProcess = false;
-  let onHandleReport = function (
-    aProcess,
-    aPath,
-    aKind,
-    aUnits,
-    aAmount,
-    aDescription
-  ) {
+  let onHandleReport = function (aProcess) {
     if (/GPU \(pid \d+\)/.test(aProcess)) {
       foundGPUProcess = true;
     }
diff --git a/toolkit/components/aboutprocesses/content/aboutProcesses.js b/toolkit/components/aboutprocesses/content/aboutProcesses.js
index 4ad00b28404a..3d80512407d7 100644
--- a/toolkit/components/aboutprocesses/content/aboutProcesses.js
+++ b/toolkit/components/aboutprocesses/content/aboutProcesses.js
@@ -787,7 +787,7 @@ var View = {
     return isOpen;
   },
 
-  displayDOMWindowRow(data, parent) {
+  displayDOMWindowRow(data) {
     const cellCount = 2;
     let rowId = "w:" + data.outerWindowId;
     let row = this._getOrCreateRow(rowId, cellCount);
@@ -1124,7 +1124,7 @@ var Control = {
     // Visibility change:
     // - stop updating while the user isn't looking;
     // - resume updating when the user returns.
-    window.addEventListener("visibilitychange", event => {
+    window.addEventListener("visibilitychange", () => {
       if (!document.hidden) {
         this._updateDisplay(true);
       }
diff --git a/toolkit/components/aboutthirdparty/tests/browser/browser_aboutthirdparty.js b/toolkit/components/aboutthirdparty/tests/browser/browser_aboutthirdparty.js
index 0a53823a35f3..865e7b949d66 100644
--- a/toolkit/components/aboutthirdparty/tests/browser/browser_aboutthirdparty.js
+++ b/toolkit/components/aboutthirdparty/tests/browser/browser_aboutthirdparty.js
@@ -135,7 +135,7 @@ add_task(async () => {
       "after system info was collected."
   );
 
-  await BrowserTestUtils.withNewTab("about:third-party", async browser => {
+  await BrowserTestUtils.withNewTab("about:third-party", async () => {
     if (!content.fetchDataDone) {
       const mainDiv = content.document.getElementById("main");
       await BrowserTestUtils.waitForMutationCondition(
diff --git a/toolkit/components/aboutwebauthn/content/aboutWebauthn.js b/toolkit/components/aboutwebauthn/content/aboutWebauthn.js
index 9142ed198a52..6232a30936c5 100644
--- a/toolkit/components/aboutwebauthn/content/aboutWebauthn.js
+++ b/toolkit/components/aboutwebauthn/content/aboutWebauthn.js
@@ -546,7 +546,7 @@ function sidebar_set_disabled(disabled) {
   });
 }
 
-function check_pin_repeat_is_correct(button) {
+function check_pin_repeat_is_correct() {
   let pin = document.getElementById("new-pin");
   let pin_repeat = document.getElementById("new-pin-repeat");
   let has_current_pin = !document.getElementById("current-pin-div").hidden;
@@ -853,7 +853,7 @@ try {
     Ci.nsIWebAuthnService
   );
   document.addEventListener("DOMContentLoaded", onLoad);
-  window.addEventListener("beforeunload", event => {
+  window.addEventListener("beforeunload", () => {
     AboutWebauthnManagerJS.uninit();
     if (AboutWebauthnService) {
       AboutWebauthnService.cancel(0);
diff --git a/toolkit/components/aboutwebauthn/tests/browser/browser_aboutwebauthn_credentials.js b/toolkit/components/aboutwebauthn/tests/browser/browser_aboutwebauthn_credentials.js
index ff45ea296284..e2b01d67efc5 100644
--- a/toolkit/components/aboutwebauthn/tests/browser/browser_aboutwebauthn_credentials.js
+++ b/toolkit/components/aboutwebauthn/tests/browser/browser_aboutwebauthn_credentials.js
@@ -24,7 +24,7 @@ registerCleanupFunction(async function () {
 function send_credential_list(credlist) {
   let num_of_creds = 0;
   credlist.forEach(domain => {
-    domain.credentials.forEach(c => {
+    domain.credentials.forEach(() => {
       num_of_creds += 1;
     });
   });
diff --git a/toolkit/components/aboutwindowsmessages/tests/browser/browser_aboutwindowsmessages.js b/toolkit/components/aboutwindowsmessages/tests/browser/browser_aboutwindowsmessages.js
index 7c667891d67b..18fbff351a2f 100644
--- a/toolkit/components/aboutwindowsmessages/tests/browser/browser_aboutwindowsmessages.js
+++ b/toolkit/components/aboutwindowsmessages/tests/browser/browser_aboutwindowsmessages.js
@@ -29,7 +29,7 @@ add_task(async () => {
   });
   await BrowserTestUtils.withNewTab(
     { gBrowser: originalBrowser, url: "about:windows-messages" },
-    async browser => {
+    async () => {
       let messagesList = content.document.getElementById("windows-div");
       // This is tricky because the test framework has its own windows
       Assert.greaterOrEqual(
diff --git a/toolkit/components/alerts/test/test_alerts_requireinteraction.html b/toolkit/components/alerts/test/test_alerts_requireinteraction.html
index ca8fa1c9e3d9..dc189920ad5e 100644
--- a/toolkit/components/alerts/test/test_alerts_requireinteraction.html
+++ b/toolkit/components/alerts/test/test_alerts_requireinteraction.html
@@ -23,7 +23,7 @@ const chromeScript = SpecialPowers.loadChromeScript(_ => {
       sendAsyncMessage("waitForXULAlert", false);
     }, 2000);
 
-    var windowObserver = function(win, aTopic, aData) {
+    var windowObserver = function(win, aTopic) {
       if (aTopic != "domwindowopened") {
         return;
       }
@@ -95,7 +95,7 @@ add_task(async function test_require_interaction() {
   var actualSequence = [];
 
   function createAlertListener(name, showCallback, finishCallback) {
-    return (subject, topic, data) => {
+    return (subject, topic) => {
       if (topic == "alertshow") {
         actualSequence.push(name + " show");
         if (showCallback) {
diff --git a/toolkit/components/alerts/test/test_invalid_utf16.html b/toolkit/components/alerts/test/test_invalid_utf16.html
index a4f862238c83..5d7fa9c0792d 100644
--- a/toolkit/components/alerts/test/test_invalid_utf16.html
+++ b/toolkit/components/alerts/test/test_invalid_utf16.html
@@ -18,7 +18,7 @@
       let promise = new Promise((res, rej) => {resolve = res; reject = rej});
 
       let success = false;
-      function observe(aSubject, aTopic, aData) {
+      function observe(aSubject, aTopic) {
         if (aTopic == "alertshow") {
           success = true;
           notifier.closeAlert(alertName);
diff --git a/toolkit/components/alerts/test/test_multiple_alerts.html b/toolkit/components/alerts/test/test_multiple_alerts.html
index 95843b2e8999..830dfdc1bb42 100644
--- a/toolkit/components/alerts/test/test_multiple_alerts.html
+++ b/toolkit/components/alerts/test/test_multiple_alerts.html
@@ -26,7 +26,7 @@ const chromeScript = SpecialPowers.loadChromeScript(_ => {
       sendAsyncMessage("waitedForPosition", null);
     }, 2000);
 
-    var windowObserver = function(win, aTopic, aData) {
+    var windowObserver = function(win, aTopic) {
       if (aTopic != "domwindowopened") {
         return;
       }
diff --git a/toolkit/components/alerts/test/test_principal.html b/toolkit/components/alerts/test/test_principal.html
index 5464d9297722..7b0795d3f8ea 100644
--- a/toolkit/components/alerts/test/test_principal.html
+++ b/toolkit/components/alerts/test/test_principal.html
@@ -38,7 +38,7 @@ const chromeScript = SpecialPowers.loadChromeScript(_ => {
 function notify(alertName, principal) {
   return new Promise((resolve, reject) => {
     var source;
-    async function observe(subject, topic, data) {
+    async function observe(subject, topic) {
       if (topic == "alertclickcallback") {
         reject(new Error("Alerts should not be clicked during test"));
       } else if (topic == "alertshow") {
diff --git a/toolkit/components/autocomplete/tests/unit/head_autocomplete.js b/toolkit/components/autocomplete/tests/unit/head_autocomplete.js
index 6aa0382d82a9..b11d02a855ba 100644
--- a/toolkit/components/autocomplete/tests/unit/head_autocomplete.js
+++ b/toolkit/components/autocomplete/tests/unit/head_autocomplete.js
@@ -101,7 +101,7 @@ AutoCompleteResultBase.prototype = {
     return this._styles[aIndex];
   },
 
-  getImageAt(aIndex) {
+  getImageAt() {
     return "";
   },
 
@@ -109,11 +109,11 @@ AutoCompleteResultBase.prototype = {
     return this._finalCompleteValues[aIndex] || this._values[aIndex];
   },
 
-  isRemovableAt(aRowIndex) {
+  isRemovableAt() {
     return true;
   },
 
-  removeValueAt(aRowIndex) {},
+  removeValueAt() {},
 
   // nsISupports implementation
   QueryInterface: ChromeUtils.generateQI(["nsIAutoCompleteResult"]),
@@ -161,7 +161,7 @@ function AutocompletePopupBase(input) {
 AutocompletePopupBase.prototype = {
   selectedIndex: 0,
   invalidate() {},
-  selectBy(reverse, page) {
+  selectBy(reverse) {
     let numRows = this.input.controller.matchCount;
     if (numRows > 0) {
       let delta = reverse ? -1 : 1;
diff --git a/toolkit/components/autocomplete/tests/unit/test_378079.js b/toolkit/components/autocomplete/tests/unit/test_378079.js
index 06819df40bc9..756783d17f2e 100644
--- a/toolkit/components/autocomplete/tests/unit/test_378079.js
+++ b/toolkit/components/autocomplete/tests/unit/test_378079.js
@@ -45,7 +45,7 @@ AutoCompleteInput.prototype = {
   popupOpen: false,
 
   popup: {
-    setSelectedIndex(aIndex) {},
+    setSelectedIndex() {},
     invalidate() {},
 
     // nsISupports implementation
@@ -100,7 +100,7 @@ AutoCompleteResult.prototype = {
     return this._styles[aIndex];
   },
 
-  getImageAt(aIndex) {
+  getImageAt() {
     return "";
   },
 
@@ -108,11 +108,11 @@ AutoCompleteResult.prototype = {
     return this.getValueAt(aIndex);
   },
 
-  isRemovableAt(aRowIndex) {
+  isRemovableAt() {
     return true;
   },
 
-  removeValueAt(aRowIndex) {},
+  removeValueAt() {},
 
   // nsISupports implementation
   QueryInterface: ChromeUtils.generateQI(["nsIAutoCompleteResult"]),
diff --git a/toolkit/components/autocomplete/tests/unit/test_393191.js b/toolkit/components/autocomplete/tests/unit/test_393191.js
index 9a0481718dda..c39a7586e95c 100644
--- a/toolkit/components/autocomplete/tests/unit/test_393191.js
+++ b/toolkit/components/autocomplete/tests/unit/test_393191.js
@@ -44,7 +44,7 @@ AutoCompleteInput.prototype = {
   popupOpen: false,
 
   popup: {
-    setSelectedIndex(aIndex) {},
+    setSelectedIndex() {},
     invalidate() {},
 
     // nsISupports implementation
@@ -99,7 +99,7 @@ AutoCompleteResult.prototype = {
     return this._styles[aIndex];
   },
 
-  getImageAt(aIndex) {
+  getImageAt() {
     return "";
   },
 
@@ -107,11 +107,11 @@ AutoCompleteResult.prototype = {
     return this.getValueAt(aIndex);
   },
 
-  isRemovableAt(aRowIndex) {
+  isRemovableAt() {
     return true;
   },
 
-  removeValueAt(aRowIndex) {},
+  removeValueAt() {},
 
   // nsISupports implementation
   QueryInterface: ChromeUtils.generateQI(["nsIAutoCompleteResult"]),
diff --git a/toolkit/components/autocomplete/tests/unit/test_440866.js b/toolkit/components/autocomplete/tests/unit/test_440866.js
index ef538cd931ce..fdc7850b2863 100644
--- a/toolkit/components/autocomplete/tests/unit/test_440866.js
+++ b/toolkit/components/autocomplete/tests/unit/test_440866.js
@@ -43,7 +43,7 @@ AutoCompleteInput.prototype = {
   popupOpen: false,
 
   popup: {
-    setSelectedIndex(aIndex) {},
+    setSelectedIndex() {},
     invalidate() {},
 
     // nsISupports implementation
@@ -98,7 +98,7 @@ AutoCompleteResult.prototype = {
     return this._styles[aIndex];
   },
 
-  getImageAt(aIndex) {
+  getImageAt() {
     return "";
   },
 
@@ -106,11 +106,11 @@ AutoCompleteResult.prototype = {
     return this.getValueAt(aIndex);
   },
 
-  isRemovableAt(aRowIndex) {
+  isRemovableAt() {
     return true;
   },
 
-  removeValueAt(aRowIndex) {},
+  removeValueAt() {},
 
   // nsISupports implementation
   QueryInterface: ChromeUtils.generateQI(["nsIAutoCompleteResult"]),
diff --git a/toolkit/components/autocomplete/tests/unit/test_autocomplete_multiple.js b/toolkit/components/autocomplete/tests/unit/test_autocomplete_multiple.js
index 68885dc4abb2..d94da5ae59b8 100644
--- a/toolkit/components/autocomplete/tests/unit/test_autocomplete_multiple.js
+++ b/toolkit/components/autocomplete/tests/unit/test_autocomplete_multiple.js
@@ -40,7 +40,7 @@ AutoCompleteInput.prototype = {
   popupOpen: false,
 
   popup: {
-    setSelectedIndex(aIndex) {},
+    setSelectedIndex() {},
     invalidate() {},
 
     // nsISupports implementation
@@ -92,7 +92,7 @@ AutoCompleteResult.prototype = {
     return this._styles[aIndex];
   },
 
-  getImageAt(aIndex) {
+  getImageAt() {
     return "";
   },
 
@@ -100,11 +100,11 @@ AutoCompleteResult.prototype = {
     return this.getValueAt(aIndex);
   },
 
-  isRemovableAt(aRowIndex) {
+  isRemovableAt() {
     return true;
   },
 
-  removeValueAt(aRowIndex) {},
+  removeValueAt() {},
 
   // nsISupports implementation
   QueryInterface: ChromeUtils.generateQI(["nsIAutoCompleteResult"]),
diff --git a/toolkit/components/autocomplete/tests/unit/test_autocomplete_userContextId.js b/toolkit/components/autocomplete/tests/unit/test_autocomplete_userContextId.js
index 4fbec408dca6..6862e63ede38 100644
--- a/toolkit/components/autocomplete/tests/unit/test_autocomplete_userContextId.js
+++ b/toolkit/components/autocomplete/tests/unit/test_autocomplete_userContextId.js
@@ -21,12 +21,7 @@ function doSearch(aString, aUserContextId) {
   return new Promise(resolve => {
     let search = new AutoCompleteSearch("test");
 
-    search.startSearch = function (
-      aSearchString,
-      aSearchParam,
-      aPreviousResult,
-      aListener
-    ) {
+    search.startSearch = function (aSearchString, aSearchParam) {
       unregisterAutoCompleteSearch(search);
       resolve(aSearchParam);
     };
diff --git a/toolkit/components/autocomplete/tests/unit/test_previousResult.js b/toolkit/components/autocomplete/tests/unit/test_previousResult.js
index 85db3f08c501..e015ff481e8f 100644
--- a/toolkit/components/autocomplete/tests/unit/test_previousResult.js
+++ b/toolkit/components/autocomplete/tests/unit/test_previousResult.js
@@ -45,7 +45,7 @@ AutoCompleteInput.prototype = {
   popupOpen: false,
 
   popup: {
-    setSelectedIndex(aIndex) {},
+    setSelectedIndex() {},
     invalidate() {},
 
     // nsISupports implementation
@@ -100,7 +100,7 @@ AutoCompleteResult.prototype = {
     return this._styles[aIndex];
   },
 
-  getImageAt(aIndex) {
+  getImageAt() {
     return "";
   },
 
@@ -108,11 +108,11 @@ AutoCompleteResult.prototype = {
     return this.getValueAt(aIndex);
   },
 
-  isRemovableAt(aRowIndex) {
+  isRemovableAt() {
     return true;
   },
 
-  removeValueAt(aRowIndex) {},
+  removeValueAt() {},
 
   // nsISupports implementation
   QueryInterface: ChromeUtils.generateQI(["nsIAutoCompleteResult"]),
diff --git a/toolkit/components/autocomplete/tests/unit/test_stopSearch.js b/toolkit/components/autocomplete/tests/unit/test_stopSearch.js
index aecf572df0a4..01bd67d63b9d 100644
--- a/toolkit/components/autocomplete/tests/unit/test_stopSearch.js
+++ b/toolkit/components/autocomplete/tests/unit/test_stopSearch.js
@@ -60,7 +60,7 @@ function AutoCompleteSearch(aName) {
 AutoCompleteSearch.prototype = {
   constructor: AutoCompleteSearch,
   stopSearchInvoked: true,
-  startSearch(aSearchString, aSearchParam, aPreviousResult, aListener) {
+  startSearch() {
     info("Check stop search has been called");
     Assert.ok(this.stopSearchInvoked);
     this.stopSearchInvoked = false;
diff --git a/toolkit/components/backgroundhangmonitor/BHRTelemetryService.sys.mjs b/toolkit/components/backgroundhangmonitor/BHRTelemetryService.sys.mjs
index 98c1274b5c55..c67552655915 100644
--- a/toolkit/components/backgroundhangmonitor/BHRTelemetryService.sys.mjs
+++ b/toolkit/components/backgroundhangmonitor/BHRTelemetryService.sys.mjs
@@ -142,7 +142,7 @@ BHRTelemetryService.prototype = Object.freeze({
     this.submit();
   },
 
-  observe(aSubject, aTopic, aData) {
+  observe(aSubject, aTopic) {
     switch (aTopic) {
       case "profile-after-change":
         this.resetPayload();
diff --git a/toolkit/components/backgroundtasks/BackgroundTask_message.sys.mjs b/toolkit/components/backgroundtasks/BackgroundTask_message.sys.mjs
index 6fc1d789b9a1..aafe4a6dcfd0 100644
--- a/toolkit/components/backgroundtasks/BackgroundTask_message.sys.mjs
+++ b/toolkit/components/backgroundtasks/BackgroundTask_message.sys.mjs
@@ -82,10 +82,7 @@ outputInfo = (sentinel, info) => {
   dump(`${sentinel}${JSON.stringify(info)}${sentinel}\n`);
 };
 
-function monkeyPatchRemoteSettingsClient({
-  last_modified = new Date().getTime(),
-  data = [],
-}) {
+function monkeyPatchRemoteSettingsClient({ data = [] }) {
   lazy.RemoteSettingsClient.prototype.get = async (options = {}) => {
     outputInfo({ "RemoteSettingsClient.get": { options, response: { data } } });
     return data;
diff --git a/toolkit/components/backgroundtasks/BackgroundTasksManager.sys.mjs b/toolkit/components/backgroundtasks/BackgroundTasksManager.sys.mjs
index dcf17625f7cb..97b2f4d93dfd 100644
--- a/toolkit/components/backgroundtasks/BackgroundTasksManager.sys.mjs
+++ b/toolkit/components/backgroundtasks/BackgroundTasksManager.sys.mjs
@@ -172,7 +172,7 @@ export class BackgroundTasksManager {
     const waitFlag =
       commandLine.findFlag("wait-for-jsdebugger", CASE_INSENSITIVE) != -1;
     if (waitFlag) {
-      function onDevtoolsThreadReady(subject, topic, data) {
+      function onDevtoolsThreadReady(subject, topic) {
         lazy.log.info(
           `${Services.appinfo.processID}: Setting breakpoints for background task named '${name}'` +
             ` (with ${commandLine.length} arguments)`
diff --git a/toolkit/components/backgroundtasks/BackgroundTasksUtils.sys.mjs b/toolkit/components/backgroundtasks/BackgroundTasksUtils.sys.mjs
index 9521af5a5669..2ee2f085aeea 100644
--- a/toolkit/components/backgroundtasks/BackgroundTasksUtils.sys.mjs
+++ b/toolkit/components/backgroundtasks/BackgroundTasksUtils.sys.mjs
@@ -193,7 +193,7 @@ export var BackgroundTasksUtils = {
     lazy.log.info(`readPreferences: profile is locked`);
 
     let prefs = {};
-    let addPref = (kind, name, value, sticky, locked) => {
+    let addPref = (kind, name, value) => {
       if (predicate && !predicate(name)) {
         return;
       }
diff --git a/toolkit/components/backgroundtasks/tests/BackgroundTask_jsdebugger.sys.mjs b/toolkit/components/backgroundtasks/tests/BackgroundTask_jsdebugger.sys.mjs
index 45cf00a449de..9479a404ff14 100644
--- a/toolkit/components/backgroundtasks/tests/BackgroundTask_jsdebugger.sys.mjs
+++ b/toolkit/components/backgroundtasks/tests/BackgroundTask_jsdebugger.sys.mjs
@@ -11,7 +11,7 @@
  * code to exit code 0.
  */
 
-export function runBackgroundTask(commandLine) {
+export function runBackgroundTask() {
   // In the future, will be modifed by the JS debugger (to 0, success).
   var exposedExitCode = 0;
 
diff --git a/toolkit/components/backgroundtasks/tests/BackgroundTask_shouldprocessupdates.sys.mjs b/toolkit/components/backgroundtasks/tests/BackgroundTask_shouldprocessupdates.sys.mjs
index 4030f42e5dd9..0b47970deee6 100644
--- a/toolkit/components/backgroundtasks/tests/BackgroundTask_shouldprocessupdates.sys.mjs
+++ b/toolkit/components/backgroundtasks/tests/BackgroundTask_shouldprocessupdates.sys.mjs
@@ -3,7 +3,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-export async function runBackgroundTask(commandLine) {
+export async function runBackgroundTask() {
   const get = Services.env.get("MOZ_TEST_PROCESS_UPDATES");
   let exitCode = 81;
   if (get == "ShouldNotProcessUpdates(): OtherInstanceRunning") {
diff --git a/toolkit/components/backgroundtasks/tests/BackgroundTask_targeting.sys.mjs b/toolkit/components/backgroundtasks/tests/BackgroundTask_targeting.sys.mjs
index fd47d184701a..b7a9d08896c5 100644
--- a/toolkit/components/backgroundtasks/tests/BackgroundTask_targeting.sys.mjs
+++ b/toolkit/components/backgroundtasks/tests/BackgroundTask_targeting.sys.mjs
@@ -20,7 +20,7 @@ const EXCLUDED_NAMES = [
  * Return 0 (success) if all targeting getters succeed, 11 (failure)
  * otherwise.
  */
-export async function runBackgroundTask(commandLine) {
+export async function runBackgroundTask() {
   let exitCode = EXIT_CODE.SUCCESS;
 
   // Can't use `ASRouterTargeting.getEnvironmentSnapshot`, since that
diff --git a/toolkit/components/captivedetect/CaptiveDetect.sys.mjs b/toolkit/components/captivedetect/CaptiveDetect.sys.mjs
index 9008fe8a08c9..5b191eccd835 100644
--- a/toolkit/components/captivedetect/CaptiveDetect.sys.mjs
+++ b/toolkit/components/captivedetect/CaptiveDetect.sys.mjs
@@ -56,7 +56,7 @@ function URLFetcher(url, timeout) {
   xhr.onerror = function () {
     self.onerror();
   };
-  xhr.onreadystatechange = function (oEvent) {
+  xhr.onreadystatechange = function () {
     if (xhr.readyState === 4) {
       if (self._isAborted) {
         return;
@@ -181,10 +181,7 @@ function LoginObserver(captivePortalDetector) {
     observeActivity: function observeActivity(
       aHttpChannel,
       aActivityType,
-      aActivitySubtype,
-      aTimestamp,
-      aExtraSizeData,
-      aExtraStringData
+      aActivitySubtype
     ) {
       if (
         aActivityType ===
@@ -541,5 +538,5 @@ if (DEBUG) {
   };
 } else {
   // eslint-disable-next-line no-global-assign
-  debug = function (s) {};
+  debug = function () {};
 }
diff --git a/toolkit/components/captivedetect/test/unit/test_abort.js b/toolkit/components/captivedetect/test/unit/test_abort.js
index 0e0a944f9b24..5cb649b4c020 100644
--- a/toolkit/components/captivedetect/test/unit/test_abort.js
+++ b/toolkit/components/captivedetect/test/unit/test_abort.js
@@ -21,7 +21,7 @@ function xhr_handler(metadata, response) {
 }
 
 function fakeUIResponse() {
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login") {
       do_throw("should not receive captive-portal-login event");
     }
@@ -37,7 +37,7 @@ function test_abort() {
       Assert.equal(++step, 1);
       gCaptivePortalDetector.finishPreparation(kInterfaceName);
     },
-    complete: function complete(success) {
+    complete: function complete() {
       do_throw("should not execute |complete| callback");
     },
   };
diff --git a/toolkit/components/captivedetect/test/unit/test_abort_during_user_login.js b/toolkit/components/captivedetect/test/unit/test_abort_during_user_login.js
index bd0011817d09..a933caee55d9 100644
--- a/toolkit/components/captivedetect/test/unit/test_abort_during_user_login.js
+++ b/toolkit/components/captivedetect/test/unit/test_abort_during_user_login.js
@@ -51,7 +51,7 @@ function test_abort() {
       Assert.equal(++step, 1);
       gCaptivePortalDetector.finishPreparation(kInterfaceName);
     },
-    complete: function complete(success) {
+    complete: function complete() {
       do_throw("should not execute |complete| callback");
     },
   };
diff --git a/toolkit/components/captivedetect/test/unit/test_abort_ongoing_request.js b/toolkit/components/captivedetect/test/unit/test_abort_ongoing_request.js
index b209e02796bb..187e27bc5d16 100644
--- a/toolkit/components/captivedetect/test/unit/test_abort_ongoing_request.js
+++ b/toolkit/components/captivedetect/test/unit/test_abort_ongoing_request.js
@@ -22,7 +22,7 @@ function xhr_handler(metadata, response) {
 }
 
 function fakeUIResponse() {
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login") {
       let xhr = new XMLHttpRequest();
       xhr.open("GET", gServerURL + kCanonicalSitePath, true);
@@ -42,7 +42,7 @@ function test_multiple_requests_abort() {
       Assert.equal(++step, 1);
       gCaptivePortalDetector.finishPreparation(kInterfaceName);
     },
-    complete: function complete(success) {
+    complete: function complete() {
       do_throw("should not execute |complete| callback for " + kInterfaceName);
     },
   };
diff --git a/toolkit/components/captivedetect/test/unit/test_abort_pending_request.js b/toolkit/components/captivedetect/test/unit/test_abort_pending_request.js
index 16d621a06b23..db6d37d904c1 100644
--- a/toolkit/components/captivedetect/test/unit/test_abort_pending_request.js
+++ b/toolkit/components/captivedetect/test/unit/test_abort_pending_request.js
@@ -22,7 +22,7 @@ function xhr_handler(metadata, response) {
 }
 
 function fakeUIResponse() {
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login") {
       let xhr = new XMLHttpRequest();
       xhr.open("GET", gServerURL + kCanonicalSitePath, true);
@@ -56,7 +56,7 @@ function test_abort() {
         "should not execute |prepare| callback for " + kOtherInterfaceName
       );
     },
-    complete: function complete(success) {
+    complete: function complete() {
       do_throw("should not execute |complete| callback for " + kInterfaceName);
     },
   };
diff --git a/toolkit/components/captivedetect/test/unit/test_captive_portal_found.js b/toolkit/components/captivedetect/test/unit/test_captive_portal_found.js
index 2a9acb8ab0a0..056bf072eeb9 100644
--- a/toolkit/components/captivedetect/test/unit/test_captive_portal_found.js
+++ b/toolkit/components/captivedetect/test/unit/test_captive_portal_found.js
@@ -21,7 +21,7 @@ function xhr_handler(metadata, response) {
 }
 
 function fakeUIResponse() {
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login") {
       let xhr = new XMLHttpRequest();
       xhr.open("GET", gServerURL + kCanonicalSitePath, true);
@@ -31,7 +31,7 @@ function fakeUIResponse() {
     }
   }, "captive-portal-login");
 
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login-success") {
       Assert.equal(++step, 4);
       gServer.stop(do_test_finished);
diff --git a/toolkit/components/captivedetect/test/unit/test_captive_portal_found_303.js b/toolkit/components/captivedetect/test/unit/test_captive_portal_found_303.js
index 1e4ec1f97d64..deb80bc67c51 100644
--- a/toolkit/components/captivedetect/test/unit/test_captive_portal_found_303.js
+++ b/toolkit/components/captivedetect/test/unit/test_captive_portal_found_303.js
@@ -26,7 +26,7 @@ function xhr_handler(metadata, response) {
 }
 
 function fakeUIResponse() {
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login") {
       let xhr = new XMLHttpRequest();
       xhr.open("GET", gServerURL + kCanonicalSitePath, true);
@@ -36,7 +36,7 @@ function fakeUIResponse() {
     }
   }, "captive-portal-login");
 
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login-success") {
       Assert.equal(++step, 4);
       gServer.stop(function () {
diff --git a/toolkit/components/captivedetect/test/unit/test_captive_portal_not_found.js b/toolkit/components/captivedetect/test/unit/test_captive_portal_not_found.js
index 25dd5f7c991f..4f8c9615dc02 100644
--- a/toolkit/components/captivedetect/test/unit/test_captive_portal_not_found.js
+++ b/toolkit/components/captivedetect/test/unit/test_captive_portal_not_found.js
@@ -19,7 +19,7 @@ function xhr_handler(metadata, response) {
 }
 
 function fakeUIResponse() {
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic == "captive-portal-login") {
       do_throw("should not receive captive-portal-login event");
     }
diff --git a/toolkit/components/captivedetect/test/unit/test_captive_portal_not_found_404.js b/toolkit/components/captivedetect/test/unit/test_captive_portal_not_found_404.js
index 3f9d212a1f35..c6608f954896 100644
--- a/toolkit/components/captivedetect/test/unit/test_captive_portal_not_found_404.js
+++ b/toolkit/components/captivedetect/test/unit/test_captive_portal_not_found_404.js
@@ -15,7 +15,7 @@ function xhr_handler(metadata, response) {
 }
 
 function fakeUIResponse() {
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login") {
       do_throw("should not receive captive-portal-login event");
     }
diff --git a/toolkit/components/captivedetect/test/unit/test_multiple_requests.js b/toolkit/components/captivedetect/test/unit/test_multiple_requests.js
index 7778a595b0e8..4b6d6511b2cf 100644
--- a/toolkit/components/captivedetect/test/unit/test_multiple_requests.js
+++ b/toolkit/components/captivedetect/test/unit/test_multiple_requests.js
@@ -23,7 +23,7 @@ function xhr_handler(metadata, response) {
 }
 
 function fakeUIResponse() {
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login") {
       let xhr = new XMLHttpRequest();
       xhr.open("GET", gServerURL + kCanonicalSitePath, true);
@@ -33,7 +33,7 @@ function fakeUIResponse() {
     }
   }, "captive-portal-login");
 
-  Services.obs.addObserver(function observe(subject, topic, data) {
+  Services.obs.addObserver(function observe(subject, topic) {
     if (topic === "captive-portal-login-success") {
       loginSuccessCount++;
       if (loginSuccessCount > 1) {
diff --git a/toolkit/components/certviewer/content/certviewer.mjs b/toolkit/components/certviewer/content/certviewer.mjs
index 3e48a069f532..ba1c6c91440e 100644
--- a/toolkit/components/certviewer/content/certviewer.mjs
+++ b/toolkit/components/certviewer/content/certviewer.mjs
@@ -10,7 +10,7 @@ import {
   pemToDER,
 } from "chrome://global/content/certviewer/certDecoder.mjs";
 
-document.addEventListener("DOMContentLoaded", async e => {
+document.addEventListener("DOMContentLoaded", async () => {
   let url = new URL(document.URL);
   let certInfo = url.searchParams.getAll("cert");
   if (certInfo.length === 0) {
@@ -469,7 +469,7 @@ const buildChain = async chain => {
       let adjustedCerts = certs.map(cert => adjustCertInformation(cert));
       return render(adjustedCerts, false);
     })
-    .catch(err => {
+    .catch(() => {
       render(null, true);
     });
 };
diff --git a/toolkit/components/certviewer/tests/browser/browser_openTabAndSendCertInfo.js b/toolkit/components/certviewer/tests/browser/browser_openTabAndSendCertInfo.js
index c6307f529a3e..faa490eae231 100644
--- a/toolkit/components/certviewer/tests/browser/browser_openTabAndSendCertInfo.js
+++ b/toolkit/components/certviewer/tests/browser/browser_openTabAndSendCertInfo.js
@@ -63,7 +63,7 @@ function openCertDownloadDialog(cert) {
     cert,
     returnVals
   );
-  return new Promise((resolve, reject) => {
+  return new Promise(resolve => {
     win.addEventListener(
       "load",
       function () {
diff --git a/toolkit/components/certviewer/tests/browser/head.js b/toolkit/components/certviewer/tests/browser/head.js
index 2a28444f9b4d..90e3b8168f98 100644
--- a/toolkit/components/certviewer/tests/browser/head.js
+++ b/toolkit/components/certviewer/tests/browser/head.js
@@ -21,7 +21,7 @@ function is_element_visible(aElement, aMsg) {
 
 // Extracted from https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/browser/components/preferences/in-content/tests/head.js#41
 function promiseLoadSubDialog(aURL) {
-  return new Promise((resolve, reject) => {
+  return new Promise(resolve => {
     content.gSubDialog._dialogStack.addEventListener(
       "dialogopen",
       function dialogopen(aEvent) {
diff --git a/toolkit/components/cleardata/ClearDataService.sys.mjs b/toolkit/components/cleardata/ClearDataService.sys.mjs
index ba34558f7e31..2f27d99921e9 100644
--- a/toolkit/components/cleardata/ClearDataService.sys.mjs
+++ b/toolkit/components/cleardata/ClearDataService.sys.mjs
@@ -193,7 +193,7 @@ const CookieCleaner = {
       });
   },
 
-  deleteByRange(aFrom, aTo) {
+  deleteByRange(aFrom) {
     return Services.cookies.removeAllSince(aFrom);
   },
 
@@ -584,7 +584,7 @@ const DownloadsCleaner = {
 };
 
 const PasswordsCleaner = {
-  deleteByHost(aHost, aOriginAttributes) {
+  deleteByHost(aHost) {
     // Clearing by host also clears associated subdomains.
     return this._deleteInternal(aLogin =>
       Services.eTLD.hasRootDomain(aLogin.hostname, aHost)
@@ -630,7 +630,7 @@ const PasswordsCleaner = {
 };
 
 const MediaDevicesCleaner = {
-  async deleteByRange(aFrom, aTo) {
+  async deleteByRange(aFrom) {
     let mediaMgr = Cc["@mozilla.org/mediaManagerService;1"].getService(
       Ci.nsIMediaManagerService
     );
@@ -799,7 +799,7 @@ const QuotaCleaner = {
     }
   },
 
-  async deleteByHost(aHost, aOriginAttributes) {
+  async deleteByHost(aHost) {
     // XXX: The aOriginAttributes is expected to always be empty({}). Maybe have
     // a debug assertion here to ensure that?
 
@@ -872,7 +872,7 @@ const QuotaCleaner = {
         _ => /* exceptionThrown = */ false,
         _ => /* exceptionThrown = */ true
       )
-      .then(exceptionThrown => {
+      .then(() => {
         // QuotaManager: In the event of a failure, we call reject to propagate
         // the error upwards.
         return new Promise((aResolve, aReject) => {
@@ -1002,7 +1002,7 @@ const PushNotificationsCleaner = {
     });
   },
 
-  deleteByHost(aHost, aOriginAttributes) {
+  deleteByHost(aHost) {
     // Will also clear entries for subdomains of aHost. Data is cleared across
     // all origin attributes.
     return this._deleteByRootDomain(aHost);
@@ -1078,7 +1078,7 @@ const StorageAccessCleaner = {
       });
   },
 
-  async deleteByHost(aHost, aOriginAttributes) {
+  async deleteByHost(aHost) {
     // Clearing by host also clears associated subdomains.
     this._deleteInternal(({ principal }) => {
       let toBeRemoved = false;
@@ -1095,7 +1095,7 @@ const StorageAccessCleaner = {
     );
   },
 
-  async deleteByRange(aFrom, aTo) {
+  async deleteByRange(aFrom) {
     Services.perms.removeByTypeSince("storageAccessAPI", aFrom / 1000);
   },
 
@@ -1105,7 +1105,7 @@ const StorageAccessCleaner = {
 };
 
 const HistoryCleaner = {
-  deleteByHost(aHost, aOriginAttributes) {
+  deleteByHost(aHost) {
     if (!AppConstants.MOZ_PLACES) {
       return Promise.resolve();
     }
@@ -1142,7 +1142,7 @@ const HistoryCleaner = {
 };
 
 const SessionHistoryCleaner = {
-  async deleteByHost(aHost, aOriginAttributes) {
+  async deleteByHost(aHost) {
     // Session storage and history also clear subdomains of aHost.
     Services.obs.notifyObservers(null, "browser:purge-sessionStorage", aHost);
     Services.obs.notifyObservers(
@@ -1160,7 +1160,7 @@ const SessionHistoryCleaner = {
     return this.deleteByHost(aBaseDomain, {});
   },
 
-  async deleteByRange(aFrom, aTo) {
+  async deleteByRange(aFrom) {
     Services.obs.notifyObservers(
       null,
       "browser:purge-session-history",
@@ -1275,7 +1275,7 @@ const PermissionsCleaner = {
     }
   },
 
-  deleteByHost(aHost, aOriginAttributes) {
+  deleteByHost(aHost) {
     return this._deleteInternal({ host: aHost });
   },
 
@@ -1287,7 +1287,7 @@ const PermissionsCleaner = {
     return this._deleteInternal({ baseDomain: aBaseDomain });
   },
 
-  async deleteByRange(aFrom, aTo) {
+  async deleteByRange(aFrom) {
     Services.perms.removeAllSince(aFrom / 1000);
   },
 
@@ -1301,7 +1301,7 @@ const PermissionsCleaner = {
 };
 
 const PreferencesCleaner = {
-  deleteByHost(aHost, aOriginAttributes) {
+  deleteByHost(aHost) {
     // Also clears subdomains of aHost.
     return new Promise((aResolve, aReject) => {
       let cps2 = Cc["@mozilla.org/content-pref/service;1"].getService(
@@ -1328,7 +1328,7 @@ const PreferencesCleaner = {
     return this.deleteByHost(aBaseDomain, {});
   },
 
-  async deleteByRange(aFrom, aTo) {
+  async deleteByRange(aFrom) {
     let cps2 = Cc["@mozilla.org/content-pref/service;1"].getService(
       Ci.nsIContentPrefService2
     );
@@ -1477,7 +1477,7 @@ const EMECleaner = {
 };
 
 const ReportsCleaner = {
-  deleteByHost(aHost, aOriginAttributes) {
+  deleteByHost(aHost) {
     // Also clears subdomains of aHost.
     return new Promise(aResolve => {
       Services.obs.notifyObservers(null, "reporting:purge-host", aHost);
@@ -1520,7 +1520,7 @@ const ContentBlockingCleaner = {
     await this.deleteAll();
   },
 
-  deleteByRange(aFrom, aTo) {
+  deleteByRange(aFrom) {
     return lazy.TrackingDBService.clearSince(aFrom);
   },
 };
@@ -1616,7 +1616,7 @@ const IdentityCredentialStorageCleaner = {
     }
   },
 
-  async deleteByPrincipal(aPrincipal, aIsUserRequest) {
+  async deleteByPrincipal(aPrincipal) {
     if (
       Services.prefs.getBoolPref(
         "dom.security.credentialmanagement.identity.enabled",
@@ -1698,7 +1698,7 @@ const BounceTrackingProtectionStateCleaner = {
     await lazy.bounceTrackingProtection.clearAll();
   },
 
-  async deleteByPrincipal(aPrincipal, aIsUserRequest) {
+  async deleteByPrincipal(aPrincipal) {
     if (!lazy.isBounceTrackingProtectionEnabled) {
       return;
     }
@@ -1709,7 +1709,7 @@ const BounceTrackingProtectionStateCleaner = {
     );
   },
 
-  async deleteByBaseDomain(aBaseDomain, aIsUserRequest) {
+  async deleteByBaseDomain(aBaseDomain) {
     if (!lazy.isBounceTrackingProtectionEnabled) {
       return;
     }
@@ -1723,7 +1723,7 @@ const BounceTrackingProtectionStateCleaner = {
     await lazy.bounceTrackingProtection.clearByTimeRange(aFrom, aTo);
   },
 
-  async deleteByHost(aHost, aOriginAttributes) {
+  async deleteByHost(aHost) {
     if (!lazy.isBounceTrackingProtectionEnabled) {
       return;
     }
diff --git a/toolkit/components/cleardata/SiteDataTestUtils.sys.mjs b/toolkit/components/cleardata/SiteDataTestUtils.sys.mjs
index a777a19b7ddc..99bd1f72b0a9 100644
--- a/toolkit/components/cleardata/SiteDataTestUtils.sys.mjs
+++ b/toolkit/components/cleardata/SiteDataTestUtils.sys.mjs
@@ -244,10 +244,10 @@ export var SiteDataTestUtils = {
     return new Promise(resolve => {
       let data = true;
       let request = indexedDB.openForPrincipal(principal, "TestDatabase", 1);
-      request.onupgradeneeded = function (e) {
+      request.onupgradeneeded = function () {
         data = false;
       };
-      request.onsuccess = function (e) {
+      request.onsuccess = function () {
         resolve(data);
       };
     });
@@ -276,11 +276,11 @@ export var SiteDataTestUtils = {
       CacheListener.prototype = {
         QueryInterface: ChromeUtils.generateQI(["nsICacheEntryOpenCallback"]),
 
-        onCacheEntryCheck(entry) {
+        onCacheEntryCheck() {
           return Ci.nsICacheEntryOpenCallback.ENTRY_WANTED;
         },
 
-        onCacheEntryAvailable(entry, isnew, status) {
+        onCacheEntryAvailable() {
           resolve();
         },
       };
diff --git a/toolkit/components/cleardata/tests/unit/test_permissions.js b/toolkit/components/cleardata/tests/unit/test_permissions.js
index 1f46ab5015b4..450476183a7a 100644
--- a/toolkit/components/cleardata/tests/unit/test_permissions.js
+++ b/toolkit/components/cleardata/tests/unit/test_permissions.js
@@ -88,7 +88,7 @@ add_task(async function test_principal_permissions() {
   await new Promise(aResolve => {
     Services.clearData.deleteData(
       Ci.nsIClearDataService.CLEAR_PERMISSIONS,
-      value => aResolve()
+      () => aResolve()
     );
   });
 });
@@ -465,7 +465,7 @@ add_task(async function test_3rdpartystorage_permissions() {
   await new Promise(aResolve => {
     Services.clearData.deleteData(
       Ci.nsIClearDataService.CLEAR_PERMISSIONS,
-      value => aResolve()
+      () => aResolve()
     );
   });
 });
diff --git a/toolkit/components/cleardata/tests/unit/test_storage_permission.js b/toolkit/components/cleardata/tests/unit/test_storage_permission.js
index a44e9f2c6a14..5ff3e6d15c15 100644
--- a/toolkit/components/cleardata/tests/unit/test_storage_permission.js
+++ b/toolkit/components/cleardata/tests/unit/test_storage_permission.js
@@ -62,7 +62,7 @@ add_task(async function test_removing_storage_permission() {
   await new Promise(aResolve => {
     Services.clearData.deleteData(
       Ci.nsIClearDataService.CLEAR_PERMISSIONS,
-      value => aResolve()
+      () => aResolve()
     );
   });
 });
@@ -138,7 +138,7 @@ add_task(async function test_removing_storage_permission_from_principal() {
   await new Promise(aResolve => {
     Services.clearData.deleteData(
       Ci.nsIClearDataService.CLEAR_PERMISSIONS,
-      value => aResolve()
+      () => aResolve()
     );
   });
 });
@@ -240,7 +240,7 @@ add_task(async function test_removing_storage_permission_from_base_domainl() {
   await new Promise(aResolve => {
     Services.clearData.deleteData(
       Ci.nsIClearDataService.CLEAR_PERMISSIONS,
-      value => aResolve()
+      () => aResolve()
     );
   });
 });
@@ -392,7 +392,7 @@ add_task(async function test_deleteUserInteractionForClearingHistory() {
   await new Promise(aResolve => {
     Services.clearData.deleteData(
       Ci.nsIClearDataService.CLEAR_PERMISSIONS,
-      value => aResolve()
+      () => aResolve()
     );
   });
 });
diff --git a/toolkit/components/contentprefs/ContentPrefService2.sys.mjs b/toolkit/components/contentprefs/ContentPrefService2.sys.mjs
index 43fa0c4cb6b5..069229c9c512 100644
--- a/toolkit/components/contentprefs/ContentPrefService2.sys.mjs
+++ b/toolkit/components/contentprefs/ContentPrefService2.sys.mjs
@@ -39,7 +39,7 @@ export function ContentPrefService2() {
 }
 
 const cache = new ContentPrefStore();
-cache.set = function CPS_cache_set(group, name, val) {
+cache.set = function CPS_cache_set() {
   Object.getPrototypeOf(this).set.apply(this, arguments);
   let groupCount = this._groups.size;
   if (groupCount >= CACHE_MAX_GROUP_ENTRIES) {
@@ -211,7 +211,7 @@ ContentPrefService2.prototype = {
           cbHandleResult(callback, new ContentPref(grp, name, val));
         }
       },
-      onDone: (reason, ok, gotRow) => {
+      onDone: (reason, ok) => {
         if (ok) {
           for (let [pbGroup, pbName, pbVal] of pbPrefs) {
             cbHandleResult(callback, new ContentPref(pbGroup, pbName, pbVal));
@@ -1088,9 +1088,8 @@ ContentPrefService2.prototype = {
    *
    * @param subj   This value depends on topic.
    * @param topic  The backchannel "method" name.
-   * @param data   This value depends on topic.
    */
-  observe: function CPS2_observe(subj, topic, data) {
+  observe: function CPS2_observe(subj, topic) {
     switch (topic) {
       case "profile-before-change":
         this._destroy();
diff --git a/toolkit/components/contentprefs/ContentPrefServiceParent.sys.mjs b/toolkit/components/contentprefs/ContentPrefServiceParent.sys.mjs
index 66b4a0274127..13ef8e871c6e 100644
--- a/toolkit/components/contentprefs/ContentPrefServiceParent.sys.mjs
+++ b/toolkit/components/contentprefs/ContentPrefServiceParent.sys.mjs
@@ -92,7 +92,7 @@ export class ContentPrefsParent extends JSProcessActorParent {
         let actor = this;
         let args = data.args;
 
-        return new Promise(resolve => {
+        return new Promise(() => {
           let listener = {
             handleResult(pref) {
               actor.sendAsyncMessage("ContentPrefs:HandleResult", {
diff --git a/toolkit/components/contentprefs/tests/browser/browser_remoteContentPrefs.js b/toolkit/components/contentprefs/tests/browser/browser_remoteContentPrefs.js
index 00c845e488d7..0b9dd22f351a 100644
--- a/toolkit/components/contentprefs/tests/browser/browser_remoteContentPrefs.js
+++ b/toolkit/components/contentprefs/tests/browser/browser_remoteContentPrefs.js
@@ -173,7 +173,7 @@ async function runTestsForFrame(browser, isPrivate) {
         onContentPrefSet(group, name, value, isPrivate) {
           resolve({ group, name, value, isPrivate });
         },
-        onContentPrefRemoved(group, name, isPrivate) {
+        onContentPrefRemoved() {
           reject("got unexpected notification");
         },
       };
@@ -202,7 +202,7 @@ async function runTestsForFrame(browser, isPrivate) {
           info("received handleResult");
           results.push(pref);
         },
-        handleCompletion(reason) {
+        handleCompletion() {
           resolve();
         },
         handleError(rv) {
diff --git a/toolkit/components/contentprefs/tests/unit_cps2/head.js b/toolkit/components/contentprefs/tests/unit_cps2/head.js
index c500d2bf01d1..bf5dcf2bc811 100644
--- a/toolkit/components/contentprefs/tests/unit_cps2/head.js
+++ b/toolkit/components/contentprefs/tests/unit_cps2/head.js
@@ -82,7 +82,7 @@ function setWithDate(group, name, val, timestamp, context) {
   });
 }
 
-async function getDate(group, name, context) {
+async function getDate(group, name) {
   let conn = await sendMessage("db");
   let [result] = await conn.execute(
     `
@@ -158,7 +158,7 @@ async function getGlobalOK(args, expectedVal) {
   await getOKEx("getGlobal", args, expectedPrefs);
 }
 
-async function getOKEx(methodName, args, expectedPrefs, strict, context) {
+async function getOKEx(methodName, args, expectedPrefs, strict) {
   let actualPrefs = [];
   await new Promise(resolve => {
     args.push(
diff --git a/toolkit/components/contentprefs/tests/unit_cps2/test_migrationToSchema4.js b/toolkit/components/contentprefs/tests/unit_cps2/test_migrationToSchema4.js
index 916fc5549862..c5faf1a8331a 100644
--- a/toolkit/components/contentprefs/tests/unit_cps2/test_migrationToSchema4.js
+++ b/toolkit/components/contentprefs/tests/unit_cps2/test_migrationToSchema4.js
@@ -25,7 +25,7 @@ BEGIN TRANSACTION;
   CREATE INDEX prefs_idx ON prefs(groupID, settingID);
 COMMIT;`;
 
-function prepareVersion3Schema(callback) {
+function prepareVersion3Schema() {
   var dbFile = Services.dirsvc.get("ProfD", Ci.nsIFile);
   dbFile.append("content-prefs.sqlite");
 
diff --git a/toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs b/toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs
index 738f8743eea3..32f3577c9370 100644
--- a/toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs
+++ b/toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs
@@ -41,7 +41,7 @@ _TabRemovalObserver.prototype = {
 
   QueryInterface: ChromeUtils.generateQI(["nsIObserver"]),
 
-  observe(subject, topic, data) {
+  observe(subject) {
     let remoteTab = subject.QueryInterface(Ci.nsIRemoteTab);
     if (this._remoteTabIds.has(remoteTab.tabId)) {
       this._remoteTabIds.delete(remoteTab.tabId);
diff --git a/toolkit/components/crashes/CrashService.sys.mjs b/toolkit/components/crashes/CrashService.sys.mjs
index cedbca53b9d6..3634327b2e66 100644
--- a/toolkit/components/crashes/CrashService.sys.mjs
+++ b/toolkit/components/crashes/CrashService.sys.mjs
@@ -66,7 +66,7 @@ function runMinidumpAnalyzer(minidumpPath, allThreads) {
         args.unshift("--full");
       }
 
-      process.runAsync(args, args.length, (subject, topic, data) => {
+      process.runAsync(args, args.length, (subject, topic) => {
         switch (topic) {
           case "process-finished":
             gRunningProcesses.delete(process);
@@ -211,7 +211,7 @@ CrashService.prototype = Object.freeze({
     await blocker;
   },
 
-  observe(subject, topic, data) {
+  observe(subject, topic) {
     switch (topic) {
       case "profile-after-change":
         // Side-effect is the singleton is instantiated.
diff --git a/toolkit/components/crashes/tests/xpcshell/test_crash_manager.js b/toolkit/components/crashes/tests/xpcshell/test_crash_manager.js
index 2f77ea51053b..e776b8f87a20 100644
--- a/toolkit/components/crashes/tests/xpcshell/test_crash_manager.js
+++ b/toolkit/components/crashes/tests/xpcshell/test_crash_manager.js
@@ -824,7 +824,7 @@ add_task(async function test_glean_crash_ping() {
 
   // Test with additional fields
   submitted = false;
-  GleanPings.crash.testBeforeNextSubmit(reason => {
+  GleanPings.crash.testBeforeNextSubmit(() => {
     submitted = true;
     const MINUTES = new Date(DUMMY_DATE_2);
     MINUTES.setSeconds(0);
diff --git a/toolkit/components/crashes/tests/xpcshell/test_crash_service.js b/toolkit/components/crashes/tests/xpcshell/test_crash_service.js
index 63ff3343d648..66482307854a 100644
--- a/toolkit/components/crashes/tests/xpcshell/test_crash_service.js
+++ b/toolkit/components/crashes/tests/xpcshell/test_crash_service.js
@@ -170,7 +170,7 @@ add_task(async function test_addCrash_quitting() {
   await setup(firstCrashId);
 
   let minidumpAnalyzerKilledPromise = new Promise((resolve, reject) => {
-    Services.obs.addObserver((subject, topic, data) => {
+    Services.obs.addObserver((subject, topic) => {
       if (topic === "test-minidump-analyzer-killed") {
         resolve();
       }
diff --git a/toolkit/components/crashes/tests/xpcshell/test_crash_store.js b/toolkit/components/crashes/tests/xpcshell/test_crash_store.js
index 515aec86a073..9aa1bca2eb37 100644
--- a/toolkit/components/crashes/tests/xpcshell/test_crash_store.js
+++ b/toolkit/components/crashes/tests/xpcshell/test_crash_store.js
@@ -257,7 +257,7 @@ add_task(async function test_add_mixed_types() {
         allAdd &&
         s.addCrash(ptName, CRASH_TYPE_CRASH, ptName + "crash", new Date());
     },
-    (_, ptName) => {
+    _ => {
       allAdd =
         allAdd &&
         s.addCrash(
diff --git a/toolkit/components/crashmonitor/CrashMonitor.sys.mjs b/toolkit/components/crashmonitor/CrashMonitor.sys.mjs
index c4dfdcbd83ed..a23446f45c80 100644
--- a/toolkit/components/crashmonitor/CrashMonitor.sys.mjs
+++ b/toolkit/components/crashmonitor/CrashMonitor.sys.mjs
@@ -189,7 +189,7 @@ export var CrashMonitor = {
    *
    * Update checkpoint file for every new notification received.
    */
-  observe(aSubject, aTopic, aData) {
+  observe(aSubject, aTopic) {
     this.writeCheckpoint(aTopic);
 
     if (
diff --git a/toolkit/components/crashmonitor/nsCrashMonitor.sys.mjs b/toolkit/components/crashmonitor/nsCrashMonitor.sys.mjs
index 0e91fc08598a..008b0e7bc833 100644
--- a/toolkit/components/crashmonitor/nsCrashMonitor.sys.mjs
+++ b/toolkit/components/crashmonitor/nsCrashMonitor.sys.mjs
@@ -14,7 +14,7 @@ CrashMonitor.prototype = {
 
   QueryInterface: ChromeUtils.generateQI(["nsIObserver"]),
 
-  observe(aSubject, aTopic, aData) {
+  observe(aSubject, aTopic) {
     switch (aTopic) {
       case "profile-after-change":
         MonitorAPI.init();
diff --git a/toolkit/components/ctypes/tests/chrome/xpcshellTestHarnessAdaptor.js b/toolkit/components/ctypes/tests/chrome/xpcshellTestHarnessAdaptor.js
index 9e90b2256138..24f0cb2602ab 100644
--- a/toolkit/components/ctypes/tests/chrome/xpcshellTestHarnessAdaptor.js
+++ b/toolkit/components/ctypes/tests/chrome/xpcshellTestHarnessAdaptor.js
@@ -83,7 +83,7 @@ FileFaker.prototype = {
   },
 };
 
-function do_get_file(path, allowNonexistent) {
+function do_get_file(path) {
   if (!_WORKINGDIR_) {
     do_throw("No way to fake files if working directory is unknown!");
   }
diff --git a/toolkit/components/ctypes/tests/unit/test_jsctypes.js b/toolkit/components/ctypes/tests/unit/test_jsctypes.js
index 7227ec992567..66255d85b1f8 100644
--- a/toolkit/components/ctypes/tests/unit/test_jsctypes.js
+++ b/toolkit/components/ctypes/tests/unit/test_jsctypes.js
@@ -3470,7 +3470,7 @@ function run_string_tests(library) {
   Assert.equal(ptrValue(test_ansi_echo(null)), 0);
 }
 
-function run_readstring_tests(library) {
+function run_readstring_tests() {
   // ASCII decode test, "hello world"
   let ascii_string = ctypes.unsigned_char.array(12)();
   ascii_string[0] = 0x68;
diff --git a/toolkit/components/enterprisepolicies/EnterprisePoliciesParent.sys.mjs b/toolkit/components/enterprisepolicies/EnterprisePoliciesParent.sys.mjs
index 15fa2193c611..00a5381133f8 100644
--- a/toolkit/components/enterprisepolicies/EnterprisePoliciesParent.sys.mjs
+++ b/toolkit/components/enterprisepolicies/EnterprisePoliciesParent.sys.mjs
@@ -296,7 +296,7 @@ EnterprisePoliciesManager.prototype = {
   },
 
   // nsIObserver implementation
-  observe: function BG_observe(subject, topic, data) {
+  observe: function BG_observe(subject, topic) {
     switch (topic) {
       case "policies-startup":
         // Before the first set of policy callbacks runs, we must
diff --git a/toolkit/components/enterprisepolicies/tests/browser/browser_policies_enterprise_only.js b/toolkit/components/enterprisepolicies/tests/browser/browser_policies_enterprise_only.js
index 3da3d250c60d..c0fd63870ac9 100644
--- a/toolkit/components/enterprisepolicies/tests/browser/browser_policies_enterprise_only.js
+++ b/toolkit/components/enterprisepolicies/tests/browser/browser_policies_enterprise_only.js
@@ -14,13 +14,13 @@ add_task(async function test_enterprise_only_policies() {
     enterprisePolicyRan = false;
 
   Policies.NormalPolicy = {
-    onProfileAfterChange(manager, param) {
+    onProfileAfterChange() {
       normalPolicyRan = true;
     },
   };
 
   Policies.EnterpriseOnlyPolicy = {
-    onProfileAfterChange(manager, param) {
+    onProfileAfterChange() {
       enterprisePolicyRan = true;
     },
   };
diff --git a/toolkit/components/forgetaboutsite/test/unit/head_forgetaboutsite.js b/toolkit/components/forgetaboutsite/test/unit/head_forgetaboutsite.js
index 0e0e178e9619..93d72aece384 100644
--- a/toolkit/components/forgetaboutsite/test/unit/head_forgetaboutsite.js
+++ b/toolkit/components/forgetaboutsite/test/unit/head_forgetaboutsite.js
@@ -21,7 +21,7 @@ async function cleanUp() {
   await new Promise(resolve => {
     Services.clearData.deleteData(
       Ci.nsIClearDataService.CLEAR_PERMISSIONS,
-      value => resolve()
+      () => resolve()
     );
   });
 }
diff --git a/toolkit/components/gfx/SanityTest.sys.mjs b/toolkit/components/gfx/SanityTest.sys.mjs
index f519735a1a09..6fe7c4e0a4f6 100644
--- a/toolkit/components/gfx/SanityTest.sys.mjs
+++ b/toolkit/components/gfx/SanityTest.sys.mjs
@@ -397,7 +397,7 @@ SanityTest.prototype = {
     return true;
   },
 
-  observe(subject, topic, data) {
+  observe(subject, topic) {
     if (topic != "profile-after-change") {
       return;
     }
diff --git a/toolkit/components/gfx/content/gfxFrameScript.js b/toolkit/components/gfx/content/gfxFrameScript.js
index c423fb8a2d98..0587f2fad7bd 100644
--- a/toolkit/components/gfx/content/gfxFrameScript.js
+++ b/toolkit/components/gfx/content/gfxFrameScript.js
@@ -45,7 +45,7 @@ const gfxFrameScript = {
     return aUri.endsWith("/sanitytest.html");
   },
 
-  onStateChange(webProgress, req, flags, status) {
+  onStateChange(webProgress, req, flags) {
     if (
       webProgress.isTopLevel &&
       flags & Ci.nsIWebProgressListener.STATE_STOP &&
diff --git a/toolkit/components/httpsonlyerror/tests/browser/browser_exception.js b/toolkit/components/httpsonlyerror/tests/browser/browser_exception.js
index 7cf98b467fb3..0c2bd4fff571 100644
--- a/toolkit/components/httpsonlyerror/tests/browser/browser_exception.js
+++ b/toolkit/components/httpsonlyerror/tests/browser/browser_exception.js
@@ -139,7 +139,7 @@ function setupFileServer() {
       "GET",
       `${SECURE_ROOT_PATH}file_upgrade_insecure_server.sjs?queryresult=${INSECURE_ROOT_PATH}`
     );
-    xhrRequest.onload = function (e) {
+    xhrRequest.onload = function () {
       var results = xhrRequest.responseText.split(",");
       resolve(results);
     };
diff --git a/toolkit/components/mediasniffer/test/unit/test_mediasniffer.js b/toolkit/components/mediasniffer/test/unit/test_mediasniffer.js
index 12aa56a85535..dc92c90a4588 100644
--- a/toolkit/components/mediasniffer/test/unit/test_mediasniffer.js
+++ b/toolkit/components/mediasniffer/test/unit/test_mediasniffer.js
@@ -71,7 +71,7 @@ var listener = {
     );
   },
 
-  onDataAvailable(request, stream, offset, count) {
+  onDataAvailable(request, stream) {
     try {
       var bis = Cc["@mozilla.org/binaryinputstream;1"].createInstance(
         Ci.nsIBinaryInputStream
@@ -83,7 +83,7 @@ var listener = {
     }
   },
 
-  onStopRequest(request, status) {
+  onStopRequest() {
     testRan++;
     runNext();
   },
diff --git a/toolkit/components/mediasniffer/test/unit/test_mediasniffer_ext.js b/toolkit/components/mediasniffer/test/unit/test_mediasniffer_ext.js
index f48ffbb75a93..5b6b400ed173 100644
--- a/toolkit/components/mediasniffer/test/unit/test_mediasniffer_ext.js
+++ b/toolkit/components/mediasniffer/test/unit/test_mediasniffer_ext.js
@@ -61,7 +61,7 @@ var listener = {
     );
   },
 
-  onDataAvailable(request, stream, offset, count) {
+  onDataAvailable(request, stream) {
     try {
       var bis = Cc["@mozilla.org/binaryinputstream;1"].createInstance(
         Ci.nsIBinaryInputStream
@@ -73,7 +73,7 @@ var listener = {
     }
   },
 
-  onStopRequest(request, status) {
+  onStopRequest() {
     testRan++;
     runNext();
   },
diff --git a/toolkit/components/messaging-system/lib/SpecialMessageActions.sys.mjs b/toolkit/components/messaging-system/lib/SpecialMessageActions.sys.mjs
index 8ed488ff88b8..41f5f9a63e68 100644
--- a/toolkit/components/messaging-system/lib/SpecialMessageActions.sys.mjs
+++ b/toolkit/components/messaging-system/lib/SpecialMessageActions.sys.mjs
@@ -291,7 +291,7 @@ export const SpecialMessageActions = {
           Ci.nsISupportsWeakReference,
         ]),
 
-        observe(aSubject, aTopic, aData) {
+        observe() {
           let state = lazy.UIState.get();
           if (state.status === lazy.UIState.STATUS_SIGNED_IN) {
             // We completed sign-in, so tear down our listener / observer and resolve
diff --git a/toolkit/components/messaging-system/schemas/SpecialMessageActionSchemas/test/browser/browser_sma_open_protection_panel.js b/toolkit/components/messaging-system/schemas/SpecialMessageActionSchemas/test/browser/browser_sma_open_protection_panel.js
index c9522426a2c7..bddc456539c6 100644
--- a/toolkit/components/messaging-system/schemas/SpecialMessageActionSchemas/test/browser/browser_sma_open_protection_panel.js
+++ b/toolkit/components/messaging-system/schemas/SpecialMessageActionSchemas/test/browser/browser_sma_open_protection_panel.js
@@ -4,7 +4,7 @@
 "use strict";
 
 add_task(async function test_OPEN_PROTECTION_PANEL() {
-  await BrowserTestUtils.withNewTab(EXAMPLE_URL, async browser => {
+  await BrowserTestUtils.withNewTab(EXAMPLE_URL, async () => {
     const popupshown = BrowserTestUtils.waitForEvent(
       window,
       "popupshown",
diff --git a/toolkit/components/messaging-system/schemas/SpecialMessageActionSchemas/test/browser/browser_sma_pin_current_tab.js b/toolkit/components/messaging-system/schemas/SpecialMessageActionSchemas/test/browser/browser_sma_pin_current_tab.js
index 442532552612..2cb0e3000f45 100644
--- a/toolkit/components/messaging-system/schemas/SpecialMessageActionSchemas/test/browser/browser_sma_pin_current_tab.js
+++ b/toolkit/components/messaging-system/schemas/SpecialMessageActionSchemas/test/browser/browser_sma_pin_current_tab.js
@@ -4,7 +4,7 @@
 "use strict";
 
 add_task(async function test_PIN_CURRENT_TAB() {
-  await BrowserTestUtils.withNewTab("about:blank", async browser => {
+  await BrowserTestUtils.withNewTab("about:blank", async () => {
     await SMATestUtils.executeAndValidateAction({ type: "PIN_CURRENT_TAB" });
 
     ok(gBrowser.selectedTab.pinned, "should pin current tab");
diff --git a/toolkit/components/ml/actors/MLEngineParent.sys.mjs b/toolkit/components/ml/actors/MLEngineParent.sys.mjs
index 10b4eed4fa16..05203e5f6920 100644
--- a/toolkit/components/ml/actors/MLEngineParent.sys.mjs
+++ b/toolkit/components/ml/actors/MLEngineParent.sys.mjs
@@ -91,7 +91,7 @@ export class MLEngineParent extends JSWindowActorParent {
   }
 
   // eslint-disable-next-line consistent-return
-  async receiveMessage({ name, data }) {
+  async receiveMessage({ name }) {
     switch (name) {
       case "MLEngine:Ready":
         if (lazy.EngineProcess.resolveMLEngineParent) {
diff --git a/toolkit/components/pdfjs/content/PdfJs.sys.mjs b/toolkit/components/pdfjs/content/PdfJs.sys.mjs
index fd6757737e69..430a153ae2d0 100644
--- a/toolkit/components/pdfjs/content/PdfJs.sys.mjs
+++ b/toolkit/components/pdfjs/content/PdfJs.sys.mjs
@@ -242,7 +242,7 @@ export var PdfJs = {
   },
 
   // nsIObserver
-  observe(aSubject, aTopic, aData) {
+  observe() {
     this.checkIsDefault();
   },
 };
diff --git a/toolkit/components/pdfjs/content/PdfJsNetwork.sys.mjs b/toolkit/components/pdfjs/content/PdfJsNetwork.sys.mjs
index dd3ebc6bf5b3..2f0d428f1857 100644
--- a/toolkit/components/pdfjs/content/PdfJsNetwork.sys.mjs
+++ b/toolkit/components/pdfjs/content/PdfJsNetwork.sys.mjs
@@ -79,7 +79,7 @@ export class NetworkManager {
     xhr.responseType = "arraybuffer";
 
     if (args.onError) {
-      xhr.onerror = function (evt) {
+      xhr.onerror = function () {
         args.onError(xhr.status);
       };
     }
@@ -109,7 +109,7 @@ export class NetworkManager {
     }
   }
 
-  onStateChange(xhrId, evt) {
+  onStateChange(xhrId) {
     var pendingRequest = this.pendingRequests[xhrId];
     if (!pendingRequest) {
       // Maybe abortRequest was called...
diff --git a/toolkit/components/pdfjs/content/PdfStreamConverter.sys.mjs b/toolkit/components/pdfjs/content/PdfStreamConverter.sys.mjs
index 257ca269b4ea..cb453935edd4 100644
--- a/toolkit/components/pdfjs/content/PdfStreamConverter.sys.mjs
+++ b/toolkit/components/pdfjs/content/PdfStreamConverter.sys.mjs
@@ -253,7 +253,7 @@ class ChromeActions {
     }
   }
 
-  download(data, sendResponse) {
+  download(data) {
     const { originalUrl, options } = data;
     const blobUrl = data.blobUrl || originalUrl;
     let { filename } = data;
@@ -318,7 +318,7 @@ class ChromeActions {
     actor.sendAsyncMessage("PDFJS:Parent:getNimbus");
     Services.obs.addObserver(
       {
-        observe(aSubject, aTopic, aData) {
+        observe(aSubject, aTopic) {
           if (aTopic === "pdfjs-getNimbus") {
             Services.obs.removeObserver(this, aTopic);
             sendResponse(aSubject && JSON.stringify(aSubject.wrappedJSObject));
@@ -747,7 +747,7 @@ PdfStreamConverter.prototype = {
    */
 
   // nsIStreamConverter::convert
-  convert(aFromStream, aFromType, aToType, aCtxt) {
+  convert() {
     throw Components.Exception("", Cr.NS_ERROR_NOT_IMPLEMENTED);
   },
 
@@ -1020,7 +1020,7 @@ PdfStreamConverter.prototype = {
     // request(aRequest) below so we don't overwrite the original channel and
     // trigger an assertion.
     var proxy = {
-      onStartRequest(request) {
+      onStartRequest() {
         listener.onStartRequest(aRequest);
       },
       onDataAvailable(request, inputStream, offset, count) {
diff --git a/toolkit/components/pdfjs/content/PdfjsParent.sys.mjs b/toolkit/components/pdfjs/content/PdfjsParent.sys.mjs
index a11d68ef021a..32bb3d65b787 100644
--- a/toolkit/components/pdfjs/content/PdfjsParent.sys.mjs
+++ b/toolkit/components/pdfjs/content/PdfjsParent.sys.mjs
@@ -187,7 +187,7 @@ export class PdfjsParent extends JSWindowActorParent {
       let newBrowser = aEvent.detail;
       newBrowser.addEventListener(
         "EndSwapDocShells",
-        evt => {
+        () => {
           this._hookupEventListeners(newBrowser);
         },
         { once: true }
diff --git a/toolkit/components/pdfjs/test/browser_pdfjs_find.js b/toolkit/components/pdfjs/test/browser_pdfjs_find.js
index 24a3a5096758..b3b3e11152c4 100644
--- a/toolkit/components/pdfjs/test/browser_pdfjs_find.js
+++ b/toolkit/components/pdfjs/test/browser_pdfjs_find.js
@@ -13,7 +13,7 @@ const OS_PDF_URL = TESTROOT + "file_pdfjs_object_stream.pdf";
 const TEST_PDF_URL = TESTROOT + "file_pdfjs_test.pdf";
 
 add_task(async function test_find_octet_stream_pdf() {
-  await BrowserTestUtils.withNewTab(OS_PDF_URL, async browser => {
+  await BrowserTestUtils.withNewTab(OS_PDF_URL, async () => {
     let findEls = ["cmd_find", "cmd_findAgain", "cmd_findPrevious"].map(id =>
       document.getElementById(id)
     );
diff --git a/toolkit/components/pdfjs/test/browser_pdfjs_force_opening_files.js b/toolkit/components/pdfjs/test/browser_pdfjs_force_opening_files.js
index 0490a6eec3fd..f09581daa7ad 100644
--- a/toolkit/components/pdfjs/test/browser_pdfjs_force_opening_files.js
+++ b/toolkit/components/pdfjs/test/browser_pdfjs_force_opening_files.js
@@ -13,7 +13,7 @@ add_task(async function test_file_opening() {
   // the default - because files from disk should always use pdfjs, unless
   // it is forcibly disabled.
   let openedWindow = false;
-  let windowOpenedPromise = new Promise((resolve, reject) => {
+  let windowOpenedPromise = new Promise(resolve => {
     addWindowListener(
       "chrome://mozapps/content/downloads/unknownContentType.xhtml",
       () => {
@@ -82,7 +82,7 @@ function addWindowListener(aURL, aCallback) {
         aCallback();
       }, domwindow);
     },
-    onCloseWindow(aXULWindow) {},
+    onCloseWindow() {},
   };
   Services.wm.addListener(listener);
   listenerCleanup = () => Services.wm.removeListener(listener);
diff --git a/toolkit/components/pdfjs/test/browser_pdfjs_fullscreen.js b/toolkit/components/pdfjs/test/browser_pdfjs_fullscreen.js
index d53e4cfa7470..4add7a471580 100644
--- a/toolkit/components/pdfjs/test/browser_pdfjs_fullscreen.js
+++ b/toolkit/components/pdfjs/test/browser_pdfjs_fullscreen.js
@@ -8,7 +8,7 @@ function waitForFullScreenState(browser, state) {
   return new Promise(resolve => {
     let eventReceived = false;
 
-    let observe = (subject, topic, data) => {
+    let observe = () => {
       if (!eventReceived) {
         return;
       }
diff --git a/toolkit/components/pdfjs/test/browser_pdfjs_navigation.js b/toolkit/components/pdfjs/test/browser_pdfjs_navigation.js
index 9851150e8023..5fda1ac8b26d 100644
--- a/toolkit/components/pdfjs/test/browser_pdfjs_navigation.js
+++ b/toolkit/components/pdfjs/test/browser_pdfjs_navigation.js
@@ -229,7 +229,7 @@ async function contentSetUp() {
     return new Promise(resolve => {
       document.addEventListener(
         "pagerendered",
-        function (e) {
+        function () {
           document.querySelector("#viewer").click();
           resolve();
         },
diff --git a/toolkit/components/pdfjs/test/browser_pdfjs_octet_stream.js b/toolkit/components/pdfjs/test/browser_pdfjs_octet_stream.js
index da630f726c37..aca3e215e9a0 100644
--- a/toolkit/components/pdfjs/test/browser_pdfjs_octet_stream.js
+++ b/toolkit/components/pdfjs/test/browser_pdfjs_octet_stream.js
@@ -88,7 +88,7 @@ add_task(async function test_octet_stream_in_frame() {
 
   await BrowserTestUtils.withNewTab(
     { gBrowser, url: `data:text/html,<iframe src='${PDF_URL}'>` },
-    async function (newTabBrowser) {
+    async function () {
       // wait until downloadsPanel opens before continuing with test
       info("Waiting for download panel to open");
       await downloadsPanelPromise;
diff --git a/toolkit/components/pdfjs/test/browser_pdfjs_savedialog.js b/toolkit/components/pdfjs/test/browser_pdfjs_savedialog.js
index 4f0c952ebbcd..e514eaf53089 100644
--- a/toolkit/components/pdfjs/test/browser_pdfjs_savedialog.js
+++ b/toolkit/components/pdfjs/test/browser_pdfjs_savedialog.js
@@ -48,6 +48,6 @@ function addWindowListener(aURL, aCallback) {
         aCallback();
       }, domwindow);
     },
-    onCloseWindow(aXULWindow) {},
+    onCloseWindow() {},
   });
 }
diff --git a/toolkit/components/printing/content/print.js b/toolkit/components/printing/content/print.js
index 3398b28ace51..1c3be1728bd9 100644
--- a/toolkit/components/printing/content/print.js
+++ b/toolkit/components/printing/content/print.js
@@ -46,7 +46,7 @@ var logger = (function () {
   return _logger;
 })();
 
-function serializeSettings(settings, logPrefix) {
+function serializeSettings(settings) {
   let re = /^(k[A-Z]|resolution)/; // accessing settings.resolution throws an exception?
   let types = new Set(["string", "boolean", "number", "undefined"]);
   let nameValues = {};
@@ -80,7 +80,7 @@ function cancelDeferredTasks() {
 
 document.addEventListener(
   "DOMContentLoaded",
-  e => {
+  () => {
     window._initialized = PrintEventHandler.init().catch(e => console.error(e));
     ourBrowser.setAttribute("flex", "0");
     ourBrowser.setAttribute("constrainpopups", "false");
@@ -96,7 +96,7 @@ window.addEventListener("dialogclosing", () => {
 
 window.addEventListener(
   "unload",
-  e => {
+  () => {
     document.textContent = "";
   },
   { once: true }
@@ -1608,7 +1608,7 @@ function PrintUIControlMixin(superClass) {
 
     render() {}
 
-    update(settings) {}
+    update() {}
 
     dispatchSettingsChange(changedSettings) {
       this.dispatchEvent(
@@ -1628,7 +1628,7 @@ function PrintUIControlMixin(superClass) {
       );
     }
 
-    handleEvent(event) {}
+    handleEvent() {}
   };
 }
 
@@ -1863,7 +1863,7 @@ class PrintSettingCheckbox extends PrintUIControlMixin(HTMLInputElement) {
     this.checked = settings[this.settingName];
   }
 
-  handleEvent(e) {
+  handleEvent() {
     this.dispatchSettingsChange({
       [this.settingName]: this.checked,
     });
@@ -1884,7 +1884,7 @@ class PrintSettingRadio extends PrintUIControlMixin(HTMLInputElement) {
     this.checked = settings[this.settingName] == this.value;
   }
 
-  handleEvent(e) {
+  handleEvent() {
     this.dispatchSettingsChange({
       [this.settingName]: this.value,
     });
@@ -2020,7 +2020,7 @@ class CopiesInput extends PrintUIControlMixin(HTMLElement) {
     this._copiesError.hidden = true;
   }
 
-  handleEvent(e) {
+  handleEvent() {
     this._copiesError.hidden = this._copiesInput.checkValidity();
   }
 }
@@ -2679,7 +2679,7 @@ class TwistySummary extends PrintUIControlMixin(HTMLElement) {
     this.updateSummary(shouldOpen);
   }
 
-  handleEvent(e) {
+  handleEvent() {
     let willOpen = !this.isOpen;
     Services.prefs.setBoolPref("print.more-settings.open", willOpen);
     this.updateSummary(willOpen);
diff --git a/toolkit/components/printing/tests/browser_preview_navigation.js b/toolkit/components/printing/tests/browser_preview_navigation.js
index 53e54eddb05a..23b3a9b7cc05 100644
--- a/toolkit/components/printing/tests/browser_preview_navigation.js
+++ b/toolkit/components/printing/tests/browser_preview_navigation.js
@@ -23,7 +23,7 @@ async function waitForPageStatusUpdate(elem, expected, message) {
   );
 }
 
-async function waitUntilVisible(elem, visible = true) {
+async function waitUntilVisible(elem) {
   await TestUtils.waitForCondition(
     () =>
       BrowserTestUtils.isVisible(elem) && getComputedStyle(elem).opacity == "1",
diff --git a/toolkit/components/printing/tests/file_window_print_reentrant.html b/toolkit/components/printing/tests/file_window_print_reentrant.html
index 7eebd8c2fe6b..2008ffaf2714 100644
--- a/toolkit/components/printing/tests/file_window_print_reentrant.html
+++ b/toolkit/components/printing/tests/file_window_print_reentrant.html
@@ -3,7 +3,7 @@
 <script>
 let count = 0;
 onload = function() {
-  window.addEventListener('beforeprint', (event) => {
+  window.addEventListener('beforeprint', () => {
     document.getElementById("before-print-count").innerText = ++count;
     print()
   });
diff --git a/toolkit/components/printing/tests/head.js b/toolkit/components/printing/tests/head.js
index 4c8c0b26b6b5..8e8c2d1754c9 100644
--- a/toolkit/components/printing/tests/head.js
+++ b/toolkit/components/printing/tests/head.js
@@ -232,11 +232,7 @@ class PrintHelper {
     });
 
     // Mock PrintEventHandler with our Promises.
-    this.win.PrintEventHandler._showPrintDialog = (
-      window,
-      haveSelection,
-      settings
-    ) => {
+    this.win.PrintEventHandler._showPrintDialog = (window, haveSelection) => {
       this.systemDialogOpenedWithSelection = haveSelection;
       return showSystemDialogPromise;
     };
diff --git a/toolkit/components/processsingleton/MainProcessSingleton.sys.mjs b/toolkit/components/processsingleton/MainProcessSingleton.sys.mjs
index a10493f79b6b..2c93bcdc65be 100644
--- a/toolkit/components/processsingleton/MainProcessSingleton.sys.mjs
+++ b/toolkit/components/processsingleton/MainProcessSingleton.sys.mjs
@@ -10,7 +10,7 @@ MainProcessSingleton.prototype = {
     "nsISupportsWeakReference",
   ]),
 
-  observe(subject, topic, data) {
+  observe(subject, topic) {
     switch (topic) {
       case "app-startup": {
         // Imported for side-effects.
diff --git a/toolkit/components/processtools/tests/browser/browser_test_powerMetrics.js b/toolkit/components/processtools/tests/browser/browser_test_powerMetrics.js
index 93833a520743..0ebaaa969e83 100644
--- a/toolkit/components/processtools/tests/browser/browser_test_powerMetrics.js
+++ b/toolkit/components/processtools/tests/browser/browser_test_powerMetrics.js
@@ -87,16 +87,12 @@ add_task(async () => {
       let initalCpuTime = await getChildCpuTime(pid);
       let afterCpuTime;
       do {
-        await SpecialPowers.spawn(
-          firstBrowser,
-          [kBusyWaitForMs],
-          async kBusyWaitForMs => {
-            let startTime = Date.now();
-            while (Date.now() - startTime < 10) {
-              // Burn CPU time...
-            }
+        await SpecialPowers.spawn(firstBrowser, [kBusyWaitForMs], async () => {
+          let startTime = Date.now();
+          while (Date.now() - startTime < 10) {
+            // Burn CPU time...
           }
-        );
+        });
         afterCpuTime = await getChildCpuTime(pid);
       } while (afterCpuTime - initalCpuTime < kBusyWaitForMs * kNS_PER_MS);
       cpuTimeSpentOnBackgroundTab = Math.floor(
diff --git a/toolkit/components/processtools/tests/browser/browser_test_procinfo.js b/toolkit/components/processtools/tests/browser/browser_test_procinfo.js
index 07c7d5d2d02c..5a301c664a55 100644
--- a/toolkit/components/processtools/tests/browser/browser_test_procinfo.js
+++ b/toolkit/components/processtools/tests/browser/browser_test_procinfo.js
@@ -58,7 +58,7 @@ add_task(async function test_proc_info() {
 
   await BrowserTestUtils.withNewTab(
     { gBrowser, url: DUMMY_URL },
-    async function (browser) {
+    async function () {
       // We test `SAMPLE_SIZE` times to increase a tad the chance of encountering race conditions.
       for (let z = 0; z < SAMPLE_SIZE; z++) {
         let parentProc = await ChromeUtils.requestProcInfo();
diff --git a/toolkit/components/promiseworker/tests/xpcshell/data/worker.js b/toolkit/components/promiseworker/tests/xpcshell/data/worker.js
index 94b6dd17ad6f..d9939bd163e0 100644
--- a/toolkit/components/promiseworker/tests/xpcshell/data/worker.js
+++ b/toolkit/components/promiseworker/tests/xpcshell/data/worker.js
@@ -43,7 +43,7 @@ var Agent = {
     return args;
   },
 
-  throwError(msg, ...args) {
+  throwError(msg) {
     throw new Error(msg);
   },
 };
diff --git a/toolkit/components/promiseworker/tests/xpcshell/data/worker.mjs b/toolkit/components/promiseworker/tests/xpcshell/data/worker.mjs
index 98a4b0ee5b4d..91b27ac8f16b 100644
--- a/toolkit/components/promiseworker/tests/xpcshell/data/worker.mjs
+++ b/toolkit/components/promiseworker/tests/xpcshell/data/worker.mjs
@@ -30,7 +30,7 @@ var Agent = {
     return args;
   },
 
-  throwError(msg, ...args) {
+  throwError(msg) {
     throw new Error(msg);
   },
 };
diff --git a/toolkit/components/prompts/src/CommonDialog.sys.mjs b/toolkit/components/prompts/src/CommonDialog.sys.mjs
index a0812aa8eca2..ef79b9d336d4 100644
--- a/toolkit/components/prompts/src/CommonDialog.sys.mjs
+++ b/toolkit/components/prompts/src/CommonDialog.sys.mjs
@@ -193,7 +193,7 @@ CommonDialog.prototype = {
     // set the icon
     let icon = this.ui.infoIcon;
     if (icon) {
-      this.iconClass.forEach((el, idx, arr) => icon.classList.add(el));
+      this.iconClass.forEach(el => icon.classList.add(el));
     }
 
     // set default result to cancelled
diff --git a/toolkit/components/prompts/src/Prompter.sys.mjs b/toolkit/components/prompts/src/Prompter.sys.mjs
index a0b5edca2f4a..cd998b08fb97 100644
--- a/toolkit/components/prompts/src/Prompter.sys.mjs
+++ b/toolkit/components/prompts/src/Prompter.sys.mjs
@@ -1720,15 +1720,7 @@ class ModalPrompter {
     return result;
   }
 
-  asyncPromptAuth(
-    channel,
-    callback,
-    context,
-    level,
-    authInfo,
-    checkLabel,
-    checkValue
-  ) {
+  asyncPromptAuth() {
     // Nothing calls this directly; netwerk ends up going through
     // nsIPromptService::GetPrompt, which delegates to login manager.
     // Login manger handles the async bits itself, and only calls out
@@ -1786,7 +1778,7 @@ AuthPromptAdapter.prototype = {
 
   /* ----------  nsIAuthPrompt2 ---------- */
 
-  promptAuth(channel, level, authInfo, checkLabel, checkValue) {
+  promptAuth(channel, level, authInfo) {
     let message = InternalPromptUtils.makeAuthMessage(
       this.oldPrompter,
       channel,
@@ -1833,15 +1825,7 @@ AuthPromptAdapter.prototype = {
     return ok;
   },
 
-  asyncPromptAuth(
-    channel,
-    callback,
-    context,
-    level,
-    authInfo,
-    checkLabel,
-    checkValue
-  ) {
+  asyncPromptAuth() {
     throw Components.Exception("", Cr.NS_ERROR_NOT_IMPLEMENTED);
   },
 };
diff --git a/toolkit/components/prompts/test/prompt_common.js b/toolkit/components/prompts/test/prompt_common.js
index 8d583060daba..cf29f10b28db 100644
--- a/toolkit/components/prompts/test/prompt_common.js
+++ b/toolkit/components/prompts/test/prompt_common.js
@@ -160,7 +160,7 @@ function onloadPromiseFor(id) {
   return new Promise(resolve => {
     iframe.addEventListener(
       "load",
-      function (e) {
+      function () {
         resolve(true);
       },
       { once: true }
@@ -366,7 +366,7 @@ function PrompterProxy(chromeScript) {
   return new Proxy(
     {},
     {
-      get(target, prop, receiver) {
+      get(target, prop) {
         return (...args) => {
           // Array of indices of out/inout params to copy from the parent back to the caller.
           let outParams = [];
diff --git a/toolkit/components/prompts/test/test_bug619644.html b/toolkit/components/prompts/test/test_bug619644.html
index 2b424c71a684..03650d6d6d48 100644
--- a/toolkit/components/prompts/test/test_bug619644.html
+++ b/toolkit/components/prompts/test/test_bug619644.html
@@ -31,7 +31,7 @@ function inittest() {
   SimpleTest.waitForExplicitFinish();
 }
 
-function runtest(e) {
+function runtest() {
   modalType = Ci.nsIPrompt.MODAL_TYPE_CONTENT;
 
   window.removeEventListener("message", runtest);
diff --git a/toolkit/components/reader/AboutReader.sys.mjs b/toolkit/components/reader/AboutReader.sys.mjs
index 6b1c28c22830..be367ae6f29b 100644
--- a/toolkit/components/reader/AboutReader.sys.mjs
+++ b/toolkit/components/reader/AboutReader.sys.mjs
@@ -1143,7 +1143,7 @@ AboutReader.prototype = {
   /*
    * If the ReaderView banner font-dropdown is closed, open it.
    */
-  _openDropdown(dropdown, window) {
+  _openDropdown(dropdown) {
     if (dropdown.classList.contains("open")) {
       return;
     }
diff --git a/toolkit/components/reader/ReaderMode.sys.mjs b/toolkit/components/reader/ReaderMode.sys.mjs
index 4b754d88b02c..8fcc91cff729 100644
--- a/toolkit/components/reader/ReaderMode.sys.mjs
+++ b/toolkit/components/reader/ReaderMode.sys.mjs
@@ -277,7 +277,7 @@ export var ReaderMode = {
       xhr.open("GET", url, true);
       xhr.onerror = evt => reject(evt.error);
       xhr.responseType = docContentType === "text/plain" ? "text" : "document";
-      xhr.onload = evt => {
+      xhr.onload = () => {
         if (xhr.status !== 200) {
           reject("Reader mode XHR failed with status: " + xhr.status);
           histogram.add(DOWNLOAD_ERROR_XHR);
diff --git a/toolkit/components/reader/test/browser_readerMode.js b/toolkit/components/reader/test/browser_readerMode.js
index a38e0a6de692..9093aa7fc1cd 100644
--- a/toolkit/components/reader/test/browser_readerMode.js
+++ b/toolkit/components/reader/test/browser_readerMode.js
@@ -23,7 +23,7 @@ ChromeUtils.defineESModuleGetters(this, {
 add_task(async function test_reader_button() {
   registerCleanupFunction(function () {
     // Reset test prefs.
-    TEST_PREFS.forEach(([name, value]) => {
+    TEST_PREFS.forEach(([name]) => {
       Services.prefs.clearUserPref(name);
     });
     while (gBrowser.tabs.length > 1) {
diff --git a/toolkit/components/reader/test/browser_readerMode_hidden_nodes.js b/toolkit/components/reader/test/browser_readerMode_hidden_nodes.js
index d8e432a1640a..a6d058dfb10e 100644
--- a/toolkit/components/reader/test/browser_readerMode_hidden_nodes.js
+++ b/toolkit/components/reader/test/browser_readerMode_hidden_nodes.js
@@ -18,7 +18,7 @@ var readerButton = document.getElementById("reader-mode-button");
 add_task(async function test_reader_button() {
   registerCleanupFunction(function () {
     // Reset test prefs.
-    TEST_PREFS.forEach(([name, value]) => {
+    TEST_PREFS.forEach(([name]) => {
       Services.prefs.clearUserPref(name);
     });
     while (gBrowser.tabs.length > 1) {
diff --git a/toolkit/components/remotebrowserutils/tests/browser/browser_documentChannel.js b/toolkit/components/remotebrowserutils/tests/browser/browser_documentChannel.js
index f32216010be5..87bf94a59bbe 100644
--- a/toolkit/components/remotebrowserutils/tests/browser/browser_documentChannel.js
+++ b/toolkit/components/remotebrowserutils/tests/browser/browser_documentChannel.js
@@ -37,14 +37,14 @@ const EXTENSION_DATA = {
   async background() {
     browser.test.log("background script running");
     browser.webRequest.onAuthRequired.addListener(
-      async details => {
+      async () => {
         browser.test.log("webRequest onAuthRequired");
 
         // A blocking request that returns a promise exercises a codepath that
         // sets the notificationCallbacks on the channel to a JS object that we
         // can't do directly QueryObject on with expected results.
         // This triggered a crash which was fixed in bug 1528188.
-        return new Promise((resolve, reject) => {
+        return new Promise(resolve => {
           setTimeout(resolve, 0);
         });
       },
diff --git a/toolkit/components/remotebrowserutils/tests/browser/browser_httpCrossOriginOpenerPolicy.js b/toolkit/components/remotebrowserutils/tests/browser/browser_httpCrossOriginOpenerPolicy.js
index 5f3eade823fd..7ef8204246ef 100644
--- a/toolkit/components/remotebrowserutils/tests/browser/browser_httpCrossOriginOpenerPolicy.js
+++ b/toolkit/components/remotebrowserutils/tests/browser/browser_httpCrossOriginOpenerPolicy.js
@@ -106,7 +106,7 @@ function waitForDownloadWindow() {
         var domwindow = aXULWindow.docShell.domWindow;
         domwindow.addEventListener("load", downloadOnLoad, true);
       },
-      onCloseWindow: aXULWindow => {},
+      onCloseWindow: () => {},
     };
 
     Services.wm.addListener(listener);
diff --git a/toolkit/components/reportbrokensite/ReportBrokenSiteChild.sys.mjs b/toolkit/components/reportbrokensite/ReportBrokenSiteChild.sys.mjs
index 291b1defc81d..5f8ccaec3e14 100644
--- a/toolkit/components/reportbrokensite/ReportBrokenSiteChild.sys.mjs
+++ b/toolkit/components/reportbrokensite/ReportBrokenSiteChild.sys.mjs
@@ -236,7 +236,7 @@ export class ReportBrokenSiteChild extends JSWindowActorChild {
     });
   }
 
-  async #getConsoleLogs(docShell) {
+  async #getConsoleLogs() {
     return this.#getLoggedMessages()
       .flat()
       .sort((a, b) => a.timeStamp - b.timeStamp)
diff --git a/toolkit/components/reputationservice/test/unit/test_app_rep.js b/toolkit/components/reputationservice/test/unit/test_app_rep.js
index 9c381a7bebca..d28b2100efb1 100644
--- a/toolkit/components/reputationservice/test/unit/test_app_rep.js
+++ b/toolkit/components/reputationservice/test/unit/test_app_rep.js
@@ -115,7 +115,7 @@ add_task(async function test_setup() {
 
   gHttpServ = new HttpServer();
   gHttpServ.registerDirectory("/", do_get_cwd());
-  gHttpServ.registerPathHandler("/download", function (request, response) {
+  gHttpServ.registerPathHandler("/download", function (request) {
     if (gExpectedRemote) {
       let body = NetUtil.readInputStreamToString(
         request.bodyInputStream,
diff --git a/toolkit/components/reputationservice/test/unit/test_app_rep_maclinux.js b/toolkit/components/reputationservice/test/unit/test_app_rep_maclinux.js
index a89197e8ec8f..6274f8f75db6 100644
--- a/toolkit/components/reputationservice/test/unit/test_app_rep_maclinux.js
+++ b/toolkit/components/reputationservice/test/unit/test_app_rep_maclinux.js
@@ -106,7 +106,7 @@ add_task(function test_setup() {
     return blob;
   }
 
-  gHttpServer.registerPathHandler("/throw", function (request, response) {
+  gHttpServer.registerPathHandler("/throw", function () {
     do_throw("We shouldn't be getting here");
   });
 
diff --git a/toolkit/components/reputationservice/test/unit/test_app_rep_windows.js b/toolkit/components/reputationservice/test/unit/test_app_rep_windows.js
index 597810859f7e..7ab164cd2a5e 100644
--- a/toolkit/components/reputationservice/test/unit/test_app_rep_windows.js
+++ b/toolkit/components/reputationservice/test/unit/test_app_rep_windows.js
@@ -212,7 +212,7 @@ add_task(async function test_setup() {
     return blob;
   }
 
-  gHttpServer.registerPathHandler("/throw", function (request, response) {
+  gHttpServer.registerPathHandler("/throw", function () {
     do_throw("We shouldn't be getting here");
   });
 
diff --git a/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs b/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs
index 223c0259b76d..bba23df68326 100644
--- a/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs
+++ b/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs
@@ -186,7 +186,7 @@ class _RFPHelper {
     );
   }
 
-  _handleHttpOnModifyRequest(subject, data) {
+  _handleHttpOnModifyRequest(subject) {
     // If we are loading an HTTP page from content, show the
     // "request English language web pages?" prompt.
     let httpChannel = subject.QueryInterface(Ci.nsIHttpChannel);
diff --git a/toolkit/components/resistfingerprinting/tests/browser/browser_fpiServiceWorkers_fingerprinting.js b/toolkit/components/resistfingerprinting/tests/browser/browser_fpiServiceWorkers_fingerprinting.js
index 64279ae44211..aaa40a792861 100644
--- a/toolkit/components/resistfingerprinting/tests/browser/browser_fpiServiceWorkers_fingerprinting.js
+++ b/toolkit/components/resistfingerprinting/tests/browser/browser_fpiServiceWorkers_fingerprinting.js
@@ -68,7 +68,7 @@ runTestInFirstAndThirdPartyContexts(
   },
   async _ => {
     await new Promise(resolve => {
-      Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_ALL, value =>
+      Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_ALL, () =>
         resolve()
       );
     });
diff --git a/toolkit/components/resistfingerprinting/tests/browser/browser_serviceWorker_fingerprinting_webcompat.js b/toolkit/components/resistfingerprinting/tests/browser/browser_serviceWorker_fingerprinting_webcompat.js
index a9bab38e6145..eb1ab8d79538 100644
--- a/toolkit/components/resistfingerprinting/tests/browser/browser_serviceWorker_fingerprinting_webcompat.js
+++ b/toolkit/components/resistfingerprinting/tests/browser/browser_serviceWorker_fingerprinting_webcompat.js
@@ -59,7 +59,7 @@ runTestInFirstAndThirdPartyContexts(
 
   async _ => {
     await new Promise(resolve => {
-      Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_ALL, value =>
+      Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_ALL, () =>
         resolve()
       );
     });
@@ -142,7 +142,7 @@ runTestInFirstAndThirdPartyContexts(
 
   async _ => {
     await new Promise(resolve => {
-      Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_ALL, value =>
+      Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_ALL, () =>
         resolve()
       );
     });
diff --git a/toolkit/components/resistfingerprinting/tests/browser/head.js b/toolkit/components/resistfingerprinting/tests/browser/head.js
index 9d8ec199566d..e2fddaecc6a3 100644
--- a/toolkit/components/resistfingerprinting/tests/browser/head.js
+++ b/toolkit/components/resistfingerprinting/tests/browser/head.js
@@ -54,7 +54,7 @@ function countDifferencesInArrayBuffers(buffer1, buffer2) {
 
 function promiseObserver(topic) {
   return new Promise(resolve => {
-    let obs = (aSubject, aTopic, aData) => {
+    let obs = (aSubject, aTopic) => {
       Services.obs.removeObserver(obs, aTopic);
       resolve(aSubject);
     };
diff --git a/toolkit/components/shopping/content/ShoppingProduct.mjs b/toolkit/components/shopping/content/ShoppingProduct.mjs
index d457ac157975..f3890a0d7438 100644
--- a/toolkit/components/shopping/content/ShoppingProduct.mjs
+++ b/toolkit/components/shopping/content/ShoppingProduct.mjs
@@ -552,7 +552,7 @@ export class ShoppingProduct extends EventEmitter {
         false
       );
     }
-    let abortHandler = e => {
+    let abortHandler = () => {
       Glean?.shoppingProduct?.requestAborted.record();
       obliviousHttpChannel.cancel(Cr.NS_BINDING_ABORTED);
     };
diff --git a/toolkit/components/shopping/test/browser/browser_shopping_ads_test.js b/toolkit/components/shopping/test/browser/browser_shopping_ads_test.js
index 1061cf7fa677..05426a08ff5d 100644
--- a/toolkit/components/shopping/test/browser/browser_shopping_ads_test.js
+++ b/toolkit/components/shopping/test/browser/browser_shopping_ads_test.js
@@ -16,7 +16,7 @@ function recommendedAdsEventListener(eventName, sidebar) {
         content.document.querySelector("shopping-container").wrappedJSObject;
       let adEl = shoppingContainer.recommendedAdEl;
       return ContentTaskUtils.waitForEvent(adEl, name, false, null, true).then(
-        ev => null
+        () => null
       );
     }
   );
diff --git a/toolkit/components/shopping/test/browser/browser_shopping_sidebar_messages.js b/toolkit/components/shopping/test/browser/browser_shopping_sidebar_messages.js
index 969b49481d18..8cab6b49d864 100644
--- a/toolkit/components/shopping/test/browser/browser_shopping_sidebar_messages.js
+++ b/toolkit/components/shopping/test/browser/browser_shopping_sidebar_messages.js
@@ -33,7 +33,7 @@ add_task(async function test_sidebar_error() {
     await SpecialPowers.spawn(
       sidebar.querySelector("browser"),
       [],
-      async prodInfo => {
+      async () => {
         let doc = content.document;
         let shoppingContainer =
           doc.querySelector("shopping-container").wrappedJSObject;
@@ -79,7 +79,7 @@ add_task(async function test_sidebar_analysis_status_page_not_supported() {
     await SpecialPowers.spawn(
       sidebar.querySelector("browser"),
       [],
-      async prodInfo => {
+      async () => {
         let doc = content.document;
         let shoppingContainer =
           doc.querySelector("shopping-container").wrappedJSObject;
@@ -125,7 +125,7 @@ add_task(async function test_sidebar_analysis_status_unprocessable() {
     await SpecialPowers.spawn(
       sidebar.querySelector("browser"),
       [],
-      async prodInfo => {
+      async () => {
         let doc = content.document;
         let shoppingContainer =
           doc.querySelector("shopping-container").wrappedJSObject;
@@ -174,7 +174,7 @@ add_task(async function test_sidebar_analysis_status_not_enough_reviews() {
       await SpecialPowers.spawn(
         sidebar.querySelector("browser"),
         [],
-        async prodInfo => {
+        async () => {
           let doc = content.document;
           let shoppingContainer =
             doc.querySelector("shopping-container").wrappedJSObject;
diff --git a/toolkit/components/shopping/test/browser/head.js b/toolkit/components/shopping/test/browser/head.js
index af676bbc33c4..f2b303ce12af 100644
--- a/toolkit/components/shopping/test/browser/head.js
+++ b/toolkit/components/shopping/test/browser/head.js
@@ -46,7 +46,7 @@ async function promiseSidebarUpdated(sidebar, expectedProduct) {
         return !!e.detail.data && isProductCurrent();
       },
       true
-    ).then(e => true);
+    ).then(() => true);
   });
 }
 
@@ -65,7 +65,7 @@ async function promiseSidebarAdsUpdated(sidebar, expectedProduct) {
       true,
       null,
       true
-    ).then(e => true);
+    ).then(() => true);
   });
 }
 
diff --git a/toolkit/components/startup/tests/browser/browser_bug511456.js b/toolkit/components/startup/tests/browser/browser_bug511456.js
index c080a1596fa9..04152a6103eb 100644
--- a/toolkit/components/startup/tests/browser/browser_bug511456.js
+++ b/toolkit/components/startup/tests/browser/browser_bug511456.js
@@ -45,7 +45,7 @@ function test() {
         win2.close();
 
         // Leave the page the second time.
-        waitForOnBeforeUnloadDialog(browser, (btnLeave, btnStay) => {
+        waitForOnBeforeUnloadDialog(browser, btnLeave => {
           btnLeave.click();
         });
 
diff --git a/toolkit/components/startup/tests/browser/browser_bug537449.js b/toolkit/components/startup/tests/browser/browser_bug537449.js
index 1b54117a7dc2..10e54ea6d284 100644
--- a/toolkit/components/startup/tests/browser/browser_bug537449.js
+++ b/toolkit/components/startup/tests/browser/browser_bug537449.js
@@ -44,7 +44,7 @@ function test() {
           win2.close();
 
           // Leave the page the second time.
-          waitForOnBeforeUnloadDialog(browser, (btnLeave, btnStay) => {
+          waitForOnBeforeUnloadDialog(browser, btnLeave => {
             btnLeave.click();
           });
 
diff --git a/toolkit/components/taskscheduler/TaskSchedulerMacOSImpl.sys.mjs b/toolkit/components/taskscheduler/TaskSchedulerMacOSImpl.sys.mjs
index 3cd5b5c51d94..ae15738513b6 100644
--- a/toolkit/components/taskscheduler/TaskSchedulerMacOSImpl.sys.mjs
+++ b/toolkit/components/taskscheduler/TaskSchedulerMacOSImpl.sys.mjs
@@ -292,12 +292,12 @@ export var MacOSImpl = {
     return serializer.serializeToString(doc);
   },
 
-  _formatLabelForThisApp(id, options) {
+  _formatLabelForThisApp(id) {
     let installHash = lazy.XreDirProvider.getInstallHash();
     return `${AppConstants.MOZ_MACBUNDLE_ID}.${installHash}.${id}`;
   },
 
-  _labelMatchesThisApp(label, options) {
+  _labelMatchesThisApp(label) {
     let installHash = lazy.XreDirProvider.getInstallHash();
     return (
       label &&
diff --git a/toolkit/components/terminator/TerminatorTelemetry.sys.mjs b/toolkit/components/terminator/TerminatorTelemetry.sys.mjs
index 9903027436f1..81f77bfcf57b 100644
--- a/toolkit/components/terminator/TerminatorTelemetry.sys.mjs
+++ b/toolkit/components/terminator/TerminatorTelemetry.sys.mjs
@@ -57,7 +57,7 @@ nsTerminatorTelemetry.prototype = {
 
   // nsIObserver
 
-  observe: function DS_observe(aSubject, aTopic, aData) {
+  observe: function DS_observe() {
     this._wasNotified = true;
 
     (async () => {
diff --git a/toolkit/components/thumbnails/BackgroundPageThumbs.sys.mjs b/toolkit/components/thumbnails/BackgroundPageThumbs.sys.mjs
index 8467653acb86..3040adc6a1f2 100644
--- a/toolkit/components/thumbnails/BackgroundPageThumbs.sys.mjs
+++ b/toolkit/components/thumbnails/BackgroundPageThumbs.sys.mjs
@@ -219,7 +219,7 @@ export const BackgroundPageThumbs = {
         "nsISupportsWeakReference",
       ]),
     };
-    this._listener.onStateChange = (wbp, request, stateFlags, status) => {
+    this._listener.onStateChange = (wbp, request, stateFlags) => {
       if (!request) {
         return;
       }
@@ -591,7 +591,7 @@ Capture.prototype = {
             this._done(browser, null, TEL_CAPTURE_DONE_BAD_URI);
           }
         },
-        failure => {
+        () => {
           // The query can fail when a crash occurs while loading. The error causes
           // thumbnail crash tests to fail with an uninteresting error message.
         }
diff --git a/toolkit/components/thumbnails/PageThumbs.sys.mjs b/toolkit/components/thumbnails/PageThumbs.sys.mjs
index 4d103c8bd856..da7e187d858d 100644
--- a/toolkit/components/thumbnails/PageThumbs.sys.mjs
+++ b/toolkit/components/thumbnails/PageThumbs.sys.mjs
@@ -262,7 +262,7 @@ export var PageThumbs = {
           aBrowser.browsingContext.currentWindowGlobal.getActor("Thumbnails");
         return thumbnailsActor
           .sendQuery("Browser:Thumbnail:CheckState")
-          .catch(err => {
+          .catch(() => {
             return false;
           });
       }
@@ -835,7 +835,7 @@ export var PageThumbsExpiration = {
     }
   },
 
-  notify: function Expiration_notify(aTimer) {
+  notify: function Expiration_notify() {
     let urls = [];
     let filtersToWaitFor = this._filters.length;
 
diff --git a/toolkit/components/thumbnails/test/browser_thumbnails_bg_captureIfMissing.js b/toolkit/components/thumbnails/test/browser_thumbnails_bg_captureIfMissing.js
index 15cf4d706757..b3b4c1f305a8 100644
--- a/toolkit/components/thumbnails/test/browser_thumbnails_bg_captureIfMissing.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_bg_captureIfMissing.js
@@ -3,7 +3,7 @@
 
 add_task(async function thumbnails_bg_captureIfMissing() {
   let numNotifications = 0;
-  function observe(subject, topic, data) {
+  function observe(subject, topic) {
     is(topic, "page-thumbnail:create", "got expected topic");
     numNotifications += 1;
   }
diff --git a/toolkit/components/thumbnails/test/browser_thumbnails_bug727765.js b/toolkit/components/thumbnails/test/browser_thumbnails_bug727765.js
index 8e953e0ffaeb..d4dd7caca773 100644
--- a/toolkit/components/thumbnails/test/browser_thumbnails_bug727765.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_bug727765.js
@@ -21,7 +21,7 @@ add_task(async function thumbnails_bg_bug727765() {
       gBrowser,
       url: URL,
     },
-    async browser => {
+    async () => {
       await captureAndCheckColor(255, 0, 0, "we have a red thumbnail");
 
       // Check the thumbnail color of the bottom right pixel.
diff --git a/toolkit/components/thumbnails/test/browser_thumbnails_bug818225.js b/toolkit/components/thumbnails/test/browser_thumbnails_bug818225.js
index 5f557c40a419..37f9b2f7d7f3 100644
--- a/toolkit/components/thumbnails/test/browser_thumbnails_bug818225.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_bug818225.js
@@ -17,7 +17,7 @@ add_task(async function thumbnails_bg_bug818225() {
       gBrowser,
       url: URL,
     },
-    async browser => {
+    async () => {
       gBrowserThumbnails.clearTopSiteURLCache();
       await whenFileExists(URL);
     }
diff --git a/toolkit/components/thumbnails/test/browser_thumbnails_redirect.js b/toolkit/components/thumbnails/test/browser_thumbnails_redirect.js
index b77b4011c373..ba06b9e77983 100644
--- a/toolkit/components/thumbnails/test/browser_thumbnails_redirect.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_redirect.js
@@ -21,7 +21,7 @@ add_task(async function thumbnails_redirect() {
       gBrowser,
       url: URL,
     },
-    browser => {}
+    () => {}
   );
 
   // Create a tab, redirecting to a page with a red background.
@@ -30,7 +30,7 @@ add_task(async function thumbnails_redirect() {
       gBrowser,
       url: URL,
     },
-    async browser => {
+    async () => {
       await captureAndCheckColor(255, 0, 0, "we have a red thumbnail");
 
       // Wait until the referrer's thumbnail's file has been written.
diff --git a/toolkit/components/thumbnails/test/browser_thumbnails_storage.js b/toolkit/components/thumbnails/test/browser_thumbnails_storage.js
index 6a9f1ed3f65b..39d26897a256 100644
--- a/toolkit/components/thumbnails/test/browser_thumbnails_storage.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_storage.js
@@ -89,7 +89,7 @@ async function promiseCreateThumbnail() {
       gBrowser,
       url: URL,
     },
-    async browser => {
+    async () => {
       gBrowserThumbnails.clearTopSiteURLCache();
       await whenFileExists(URL);
     }
diff --git a/toolkit/components/thumbnails/test/browser_thumbnails_update.js b/toolkit/components/thumbnails/test/browser_thumbnails_update.js
index 004df9a01f25..7a00717e2f58 100644
--- a/toolkit/components/thumbnails/test/browser_thumbnails_update.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_update.js
@@ -163,7 +163,7 @@ add_task(async function thumbnails_captureAndStore_error_response() {
       gBrowser,
       url: URL,
     },
-    async browser => {
+    async () => {
       await captureAndCheckColor(0, 255, 0, "we have a green thumbnail");
     }
   );
@@ -176,7 +176,7 @@ add_task(async function thumbnails_captureAndStore_error_response() {
       gBrowser,
       url: URL,
     },
-    async browser => {
+    async () => {
       await captureAndCheckColor(0, 255, 0, "we still have a green thumbnail");
     }
   );
@@ -195,7 +195,7 @@ add_task(async function thumbnails_captureAndStore_ok_response() {
       gBrowser,
       url: URL,
     },
-    async browser => {
+    async () => {
       await captureAndCheckColor(0, 255, 0, "we have a green thumbnail");
     }
   );
@@ -208,7 +208,7 @@ add_task(async function thumbnails_captureAndStore_ok_response() {
       gBrowser,
       url: URL,
     },
-    async browser => {
+    async () => {
       await captureAndCheckColor(255, 0, 0, "we now have a red thumbnail");
     }
   );
diff --git a/toolkit/components/timermanager/UpdateTimerManager.sys.mjs b/toolkit/components/timermanager/UpdateTimerManager.sys.mjs
index 607a3b0e71c8..14c34e88473b 100644
--- a/toolkit/components/timermanager/UpdateTimerManager.sys.mjs
+++ b/toolkit/components/timermanager/UpdateTimerManager.sys.mjs
@@ -69,7 +69,7 @@ TimerManager.prototype = {
   /**
    * See nsIObserver.idl
    */
-  observe: function TM_observe(aSubject, aTopic, aData) {
+  observe: function TM_observe(aSubject, aTopic) {
     // Prevent setting the timer interval to a value of less than 30 seconds.
     var minInterval = 30000;
     // Prevent setting the first timer interval to a value of less than 10
diff --git a/toolkit/components/timermanager/tests/unit/consumerNotifications.js b/toolkit/components/timermanager/tests/unit/consumerNotifications.js
index 1e092070430f..0f20e282e4b0 100644
--- a/toolkit/components/timermanager/tests/unit/consumerNotifications.js
+++ b/toolkit/components/timermanager/tests/unit/consumerNotifications.js
@@ -142,7 +142,7 @@ ChromeUtils.defineLazyGetter(this, "gCompReg", function () {
 });
 
 const gTest0TimerCallback = {
-  notify: function T0CB_notify(aTimer) {
+  notify: function T0CB_notify() {
     // This can happen when another notification fails and this timer having
     // time to fire so check other timers are successful.
     do_throw("gTest0TimerCallback notify method should not have been called");
@@ -157,7 +157,7 @@ const gTest0Factory = {
 };
 
 const gTest1TimerCallback = {
-  notify: function T1CB_notify(aTimer) {
+  notify: function T1CB_notify() {
     // This can happen when another notification fails and this timer having
     // time to fire so check other timers are successful.
     do_throw("gTest1TimerCallback notify method should not have been called");
@@ -172,7 +172,7 @@ const gTest1Factory = {
 };
 
 const gTest2TimerCallback = {
-  notify: function T2CB_notify(aTimer) {
+  notify: function T2CB_notify() {
     // This can happen when another notification fails and this timer having
     // time to fire so check other timers are successful.
     do_throw("gTest2TimerCallback notify method should not have been called");
@@ -197,7 +197,7 @@ const gTest3Factory = {
 };
 
 const gTest4TimerCallback = {
-  notify: function T4CB_notify(aTimer) {
+  notify: function T4CB_notify() {
     Services.catMan.deleteCategoryEntry(
       CATEGORY_UPDATE_TIMER,
       TESTS[4].desc,
@@ -216,7 +216,7 @@ const gTest4Factory = {
 };
 
 const gTest5TimerCallback = {
-  notify: function T5CB_notify(aTimer) {
+  notify: function T5CB_notify() {
     Services.catMan.deleteCategoryEntry(
       CATEGORY_UPDATE_TIMER,
       TESTS[5].desc,
@@ -235,7 +235,7 @@ const gTest5Factory = {
 };
 
 const gTest6TimerCallback = {
-  notify: function T6CB_notify(aTimer) {
+  notify: function T6CB_notify() {
     Services.catMan.deleteCategoryEntry(
       CATEGORY_UPDATE_TIMER,
       TESTS[6].desc,
@@ -254,7 +254,7 @@ const gTest6Factory = {
 };
 
 const gTest7TimerCallback = {
-  notify: function T7CB_notify(aTimer) {
+  notify: function T7CB_notify() {
     Services.catMan.deleteCategoryEntry(
       CATEGORY_UPDATE_TIMER,
       TESTS[7].desc,
@@ -273,7 +273,7 @@ const gTest7Factory = {
 };
 
 const gTest8TimerCallback = {
-  notify: function T8CB_notify(aTimer) {
+  notify: function T8CB_notify() {
     TESTS[8].notified = true;
     TESTS[8].notifyTime = Date.now();
     executeSoon(function () {
@@ -290,7 +290,7 @@ const gTest8Factory = {
 };
 
 const gTest9TimerCallback = {
-  notify: function T9CB_notify(aTimer) {
+  notify: function T9CB_notify() {
     TESTS[9].notified = true;
     TESTS[9].notifyTime = Date.now();
     executeSoon(function () {
@@ -301,7 +301,7 @@ const gTest9TimerCallback = {
 };
 
 const gTest10TimerCallback = {
-  notify: function T9CB_notify(aTimer) {
+  notify: function T9CB_notify() {
     // The timer should have been unregistered before this could
     // be called.
     do_throw("gTest10TimerCallback notify method should not have been called");
diff --git a/toolkit/components/tooltiptext/tests/browser_bug581947.js b/toolkit/components/tooltiptext/tests/browser_bug581947.js
index 6e5eb9ea14fd..09717354705a 100644
--- a/toolkit/components/tooltiptext/tests/browser_bug581947.js
+++ b/toolkit/components/tooltiptext/tests/browser_bug581947.js
@@ -55,7 +55,7 @@ function todo_check(aBrowser, aElementName, aBarred) {
   return SpecialPowers.spawn(
     aBrowser,
     [[aElementName, aBarred]],
-    async function ([aElementName, aBarred]) {
+    async function ([aElementName]) {
       let e = content.document.createElement(aElementName);
       let contentElement = content.document.getElementById("content");
       contentElement.appendChild(e);
diff --git a/toolkit/components/translations/tests/browser/browser_about_translations_dropdowns.js b/toolkit/components/translations/tests/browser/browser_about_translations_dropdowns.js
index 6aed512952ed..381903e5b153 100644
--- a/toolkit/components/translations/tests/browser/browser_about_translations_dropdowns.js
+++ b/toolkit/components/translations/tests/browser/browser_about_translations_dropdowns.js
@@ -13,7 +13,7 @@ add_task(async function test_about_translations_dropdowns() {
   await openAboutTranslations({
     languagePairs,
     dataForContent: languagePairs,
-    runInPage: async ({ dataForContent: languagePairs, selectors }) => {
+    runInPage: async ({ selectors }) => {
       const { document } = content;
 
       await ContentTaskUtils.waitForCondition(
diff --git a/toolkit/components/translations/tests/browser/shared-head.js b/toolkit/components/translations/tests/browser/shared-head.js
index 82b3e783a70a..efbba0da49ee 100644
--- a/toolkit/components/translations/tests/browser/shared-head.js
+++ b/toolkit/components/translations/tests/browser/shared-head.js
@@ -1377,7 +1377,7 @@ async function waitForCloseDialogWindow(dialogWindow) {
 
 // Extracted from https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/browser/components/preferences/in-content/tests/head.js#41
 function promiseLoadSubDialog(aURL) {
-  return new Promise((resolve, reject) => {
+  return new Promise(resolve => {
     content.gSubDialog._dialogStack.addEventListener(
       "dialogopen",
       function dialogopen(aEvent) {
diff --git a/toolkit/components/utils/ClientEnvironment.sys.mjs b/toolkit/components/utils/ClientEnvironment.sys.mjs
index 1c6bbfbabaf2..64fb6da9e194 100644
--- a/toolkit/components/utils/ClientEnvironment.sys.mjs
+++ b/toolkit/components/utils/ClientEnvironment.sys.mjs
@@ -76,7 +76,7 @@ export class ClientEnvironmentBase {
     }
 
     return new Proxy(target, {
-      get(target, prop, receiver) {
+      get(target, prop) {
         if (prop == "main") {
           return target.main;
         }
diff --git a/toolkit/components/utils/SimpleServices.sys.mjs b/toolkit/components/utils/SimpleServices.sys.mjs
index a69388435c36..7c872cc7a68d 100644
--- a/toolkit/components/utils/SimpleServices.sys.mjs
+++ b/toolkit/components/utils/SimpleServices.sys.mjs
@@ -103,7 +103,7 @@ AddonLocalizationConverter.prototype = {
     this.listener = aListener;
   },
 
-  onStartRequest(aRequest) {
+  onStartRequest() {
     this.parts = [];
     this.decoder = new TextDecoder();
   },
diff --git a/toolkit/components/viewsource/test/browser/browser_contextmenu.js b/toolkit/components/viewsource/test/browser/browser_contextmenu.js
index afc8ab8c84e2..12244f7589b9 100644
--- a/toolkit/components/viewsource/test/browser/browser_contextmenu.js
+++ b/toolkit/components/viewsource/test/browser/browser_contextmenu.js
@@ -42,7 +42,7 @@ async function onViewSourceWindowOpen(aWindow) {
   gCopyEmailMenuItem = aWindow.document.getElementById("context-copyemail");
 
   let browser = gBrowser.selectedBrowser;
-  await SpecialPowers.spawn(browser, [], async function (arg) {
+  await SpecialPowers.spawn(browser, [], async function () {
     let tags = content.document.querySelectorAll("a[href]");
     Assert.equal(
       tags[0].href,
diff --git a/toolkit/components/viewsource/test/browser/browser_viewsource_newwindow.js b/toolkit/components/viewsource/test/browser/browser_viewsource_newwindow.js
index 8a38d94719f1..bdae8a92aa93 100644
--- a/toolkit/components/viewsource/test/browser/browser_viewsource_newwindow.js
+++ b/toolkit/components/viewsource/test/browser/browser_viewsource_newwindow.js
@@ -58,14 +58,14 @@ add_task(async function () {
       url: "data:text/html," + source,
       gBrowser,
     },
-    async browser => {
+    async () => {
       let winPromise = waitForNewViewSourceWindow(
         "view-source:data:text/html;charset=utf-8,%3Cp%3E%EF%B7%90test%EF%B7%AF%3C%2Fp%3E"
       );
       await SpecialPowers.spawn(
         gBrowser.selectedBrowser,
         [],
-        async function (arg) {
+        async function () {
           let element = content.document.querySelector("p");
           content.getSelection().selectAllChildren(element);
         }
diff --git a/toolkit/components/windowcreator/test/test_bug449141.html b/toolkit/components/windowcreator/test/test_bug449141.html
index f178689599ac..84ee5f67f6f5 100644
--- a/toolkit/components/windowcreator/test/test_bug449141.html
+++ b/toolkit/components/windowcreator/test/test_bug449141.html
@@ -35,7 +35,7 @@ var progressListener = {
   onProgressChange() {
     /* Ignore progress callback */
   },
-  onStateChange(aProgress, aRequest, aStateFlag, aStatus) {
+  onStateChange(aProgress, aRequest, aStateFlag) {
     if (aStateFlag & STATE_STOP) {
       var dirExists = false;
       var videoExists = false;
diff --git a/toolkit/components/windowwatcher/test/browser_new_content_window_chromeflags.js b/toolkit/components/windowwatcher/test/browser_new_content_window_chromeflags.js
index 4eff3b46f039..d14175c088ac 100644
--- a/toolkit/components/windowwatcher/test/browser_new_content_window_chromeflags.js
+++ b/toolkit/components/windowwatcher/test/browser_new_content_window_chromeflags.js
@@ -134,7 +134,7 @@ function getContentChromeFlags(win) {
  * @param chromeFlags (int)
  *        Some chromeFlags to check.
  */
-function assertContentFlags(chromeFlags, isPopup) {
+function assertContentFlags(chromeFlags) {
   for (let feature in DISALLOWED) {
     let flag = DISALLOWED[feature].flag;
     Assert.ok(flag, "Expected flag to be a non-zeroish value");
@@ -183,7 +183,7 @@ add_task(async function test_disallowed_flags() {
       gBrowser,
       url: SCRIPT_PAGE,
     },
-    async function (browser) {
+    async function () {
       let win = await newWinPromise;
       let parentChromeFlags = getParentChromeFlags(win);
       assertContentFlags(parentChromeFlags);
@@ -230,7 +230,7 @@ add_task(async function test_disallowed_flags() {
       gBrowser,
       url: SCRIPT_PAGE_FOR_CHROME_ALL,
     },
-    async function (browser) {
+    async function () {
       let win = await newWinPromise;
       let parentChromeFlags = getParentChromeFlags(win);
       Assert.notEqual(
@@ -257,7 +257,7 @@ add_task(async function test_scrollbars_flag() {
       gBrowser,
       url: SCRIPT_PAGE,
     },
-    async function (browser) {
+    async function () {
       let win = await newWinPromise;
 
       let parentChromeFlags = getParentChromeFlags(win);
diff --git a/toolkit/components/windowwatcher/test/browser_new_remote_window_flags.js b/toolkit/components/windowwatcher/test/browser_new_remote_window_flags.js
index 06a15d123c05..ae2bdc41b36d 100644
--- a/toolkit/components/windowwatcher/test/browser_new_remote_window_flags.js
+++ b/toolkit/components/windowwatcher/test/browser_new_remote_window_flags.js
@@ -61,7 +61,7 @@ add_task(async function test_new_remote_window_flags_window_open() {
       gBrowser,
       url: SCRIPT_PAGE,
     },
-    async function (browser) {
+    async function () {
       let win = await newWinPromise;
       assertFlags(win);
       await BrowserTestUtils.closeWindow(win);
diff --git a/toolkit/components/windowwatcher/test/browser_new_sized_window.js b/toolkit/components/windowwatcher/test/browser_new_sized_window.js
index 0a1e63a8c8f0..acb73f027eb3 100644
--- a/toolkit/components/windowwatcher/test/browser_new_sized_window.js
+++ b/toolkit/components/windowwatcher/test/browser_new_sized_window.js
@@ -33,7 +33,7 @@ function test_dimensions({ width, height }) {
       gBrowser,
       url: SCRIPT_PAGE,
     },
-    async function (browser) {
+    async function () {
       let win = await newWinPromise;
       let rect = win.gBrowser.selectedBrowser.getBoundingClientRect();
 
diff --git a/toolkit/components/windowwatcher/test/browser_non_popup_from_popup.js b/toolkit/components/windowwatcher/test/browser_non_popup_from_popup.js
index 9c905bacc198..b6e7f2b131a1 100644
--- a/toolkit/components/windowwatcher/test/browser_non_popup_from_popup.js
+++ b/toolkit/components/windowwatcher/test/browser_non_popup_from_popup.js
@@ -28,7 +28,7 @@ add_task(async function test_non_popup_from_popup() {
       gBrowser,
       url: BLANK_PAGE,
     },
-    async function (browser) {
+    async function () {
       // Wait for a popup opened by POPUP_OPENER.
       const newPopupPromise = BrowserTestUtils.waitForNewWindow();
 
diff --git a/toolkit/components/windowwatcher/test/head.js b/toolkit/components/windowwatcher/test/head.js
index f72344bcd0f0..d12685624473 100644
--- a/toolkit/components/windowwatcher/test/head.js
+++ b/toolkit/components/windowwatcher/test/head.js
@@ -125,7 +125,7 @@ async function testPopupPatterns(nonPopup) {
           gBrowser,
           url: BLANK_PAGE,
         },
-        async function (browser) {
+        async function () {
           const newWinPromise = BrowserTestUtils.waitForNewWindow();
           BrowserTestUtils.startLoadingURIString(gBrowser, SCRIPT_PAGE);
 
@@ -159,7 +159,7 @@ async function testPopupPatterns(nonPopup) {
           gBrowser,
           url: BLANK_PAGE,
         },
-        async function (browser) {
+        async function () {
           const newTabPromise = BrowserTestUtils.waitForNewTab(
             gBrowser,
             OPEN_PAGE
diff --git a/toolkit/components/workerloader/tests/worker_test_loading.js b/toolkit/components/workerloader/tests/worker_test_loading.js
index 551c56d7d380..d13fbed684ad 100644
--- a/toolkit/components/workerloader/tests/worker_test_loading.js
+++ b/toolkit/components/workerloader/tests/worker_test_loading.js
@@ -152,7 +152,7 @@ add_test(function test_load() {
   is(J.foo, "foo", "Module J exported value foo");
 });
 
-self.onmessage = function (message) {
+self.onmessage = function () {
   for (let test of tests) {
     info("Entering " + test.name);
     try {
diff --git a/toolkit/components/xulstore/XULStore.sys.mjs b/toolkit/components/xulstore/XULStore.sys.mjs
index 5648eedbedcb..f84cd5771271 100644
--- a/toolkit/components/xulstore/XULStore.sys.mjs
+++ b/toolkit/components/xulstore/XULStore.sys.mjs
@@ -89,7 +89,7 @@ XULStore.prototype = {
     this.readFile();
   },
 
-  observe(subject, topic, data) {
+  observe(subject, topic) {
     this.writeFile();
     if (topic == "profile-before-change") {
       this._saveAllowed = false;
diff --git a/toolkit/content/aboutLogging.js b/toolkit/content/aboutLogging.js
index daff10fbec6b..360ab366e1f1 100644
--- a/toolkit/content/aboutLogging.js
+++ b/toolkit/content/aboutLogging.js
@@ -234,7 +234,7 @@ function populatePresets() {
   $("#log-modules").value = gLoggingPresets[dropdown.value].modules;
   setPresetAndDescription(dropdown.value);
   // When changing the list switch to custom.
-  $("#log-modules").oninput = e => {
+  $("#log-modules").oninput = () => {
     dropdown.value = "custom";
   };
 }
@@ -534,7 +534,7 @@ function updateLogFile(file) {
 
     if (file.exists()) {
       openLogFileButton.disabled = false;
-      openLogFileButton.onclick = function (e) {
+      openLogFileButton.onclick = function () {
         file.reveal();
       };
     }
diff --git a/toolkit/content/aboutNetError.mjs b/toolkit/content/aboutNetError.mjs
index 554553fd62f3..1c733d5dbba0 100644
--- a/toolkit/content/aboutNetError.mjs
+++ b/toolkit/content/aboutNetError.mjs
@@ -498,7 +498,7 @@ function initPage() {
       trrExceptionButton.addEventListener("click", () => {
         RPMSendQuery("Browser:AddTRRExcludedDomain", {
           hostname: HOST_NAME,
-        }).then(msg => {
+        }).then(() => {
           retryThis(trrExceptionButton);
         });
       });
@@ -1061,15 +1061,15 @@ function addCertException() {
     () => {
       location.reload();
     },
-    err => {}
+    () => {}
   );
 }
 
-function onReturnButtonClick(e) {
+function onReturnButtonClick() {
   RPMSendAsyncMessage("Browser:SSLErrorGoBack");
 }
 
-function copyPEMToClipboard(e) {
+function copyPEMToClipboard() {
   const errorText = document.getElementById("certificateErrorText");
   navigator.clipboard.writeText(errorText.textContent);
 }
diff --git a/toolkit/content/aboutProfiles.js b/toolkit/content/aboutProfiles.js
index 15c0419a11fe..38dc86c31fd2 100644
--- a/toolkit/content/aboutProfiles.js
+++ b/toolkit/content/aboutProfiles.js
@@ -139,7 +139,7 @@ function display(profileData) {
 
         td.appendChild(button);
 
-        button.addEventListener("click", function (e) {
+        button.addEventListener("click", function () {
           value.reveal();
         });
       }
diff --git a/toolkit/content/aboutSupport.js b/toolkit/content/aboutSupport.js
index f9f35e7e76d9..6cfc20369d54 100644
--- a/toolkit/content/aboutSupport.js
+++ b/toolkit/content/aboutSupport.js
@@ -20,7 +20,7 @@ ChromeUtils.defineESModuleGetters(this, {
   ProcessType: "resource://gre/modules/ProcessType.sys.mjs",
 });
 
-window.addEventListener("load", function onload(event) {
+window.addEventListener("load", function onload() {
   try {
     window.removeEventListener("load", onload);
     Troubleshoot.snapshot().then(async snapshot => {
@@ -1051,7 +1051,7 @@ var snapshotFormatters = {
       }
       let button = $("enumerate-database-button");
       if (button) {
-        button.addEventListener("click", function (event) {
+        button.addEventListener("click", function () {
           let { KeyValueService } = ChromeUtils.importESModule(
             "resource://gre/modules/kvstore.sys.mjs"
           );
@@ -1074,7 +1074,7 @@ var snapshotFormatters = {
                 $("enumerate-database-result").textContent +=
                   logs.join("\n") + "\n";
               })
-              .catch(err => {
+              .catch(() => {
                 $("enumerate-database-result").textContent += `${name}:\n`;
               });
           }
@@ -1105,7 +1105,7 @@ var snapshotFormatters = {
             'th[data-l10n-id="roundtrip-latency"]'
           ).nextSibling.textContent = latencyString;
         })
-        .catch(e => {});
+        .catch(() => {});
     }
 
     function createCDMInfoRow(cdmInfo) {
@@ -1606,7 +1606,7 @@ function sortedArrayFromObject(obj) {
   for (let prop in obj) {
     tuples.push([prop, obj[prop]]);
   }
-  tuples.sort(([prop1, v1], [prop2, v2]) => prop1.localeCompare(prop2));
+  tuples.sort(([prop1], [prop2]) => prop1.localeCompare(prop2));
   return tuples;
 }
 
@@ -1757,7 +1757,7 @@ Serializer.prototype = {
     }
   },
 
-  _startNewLine(lines) {
+  _startNewLine() {
     let currLine = this._currentLine;
     if (currLine) {
       // The current line is not empty.  Trim it.
@@ -1770,7 +1770,7 @@ Serializer.prototype = {
     this._lines.push("");
   },
 
-  _appendText(text, lines) {
+  _appendText(text) {
     this._currentLine += text;
   },
 
@@ -1926,13 +1926,13 @@ function safeModeRestart() {
 function setupEventListeners() {
   let button = $("reset-box-button");
   if (button) {
-    button.addEventListener("click", function (event) {
+    button.addEventListener("click", function () {
       ResetProfile.openConfirmationDialog(window);
     });
   }
   button = $("clear-startup-cache-button");
   if (button) {
-    button.addEventListener("click", async function (event) {
+    button.addEventListener("click", async function () {
       const [promptTitle, promptBody, restartButtonLabel] =
         await document.l10n.formatValues([
           { id: "startup-cache-dialog-title2" },
@@ -1965,7 +1965,7 @@ function setupEventListeners() {
   }
   button = $("restart-in-safe-mode-button");
   if (button) {
-    button.addEventListener("click", function (event) {
+    button.addEventListener("click", function () {
       if (
         Services.obs
           .enumerateObservers("restart-in-safe-mode")
@@ -1983,7 +1983,7 @@ function setupEventListeners() {
   if (AppConstants.MOZ_UPDATER) {
     button = $("update-dir-button");
     if (button) {
-      button.addEventListener("click", function (event) {
+      button.addEventListener("click", function () {
         // Get the update directory.
         let updateDir = Services.dirsvc.get("UpdRootD", Ci.nsIFile);
         if (!updateDir.exists()) {
@@ -2001,7 +2001,7 @@ function setupEventListeners() {
     }
     button = $("show-update-history-button");
     if (button) {
-      button.addEventListener("click", function (event) {
+      button.addEventListener("click", function () {
         window.browsingContext.topChromeWindow.openDialog(
           "chrome://mozapps/content/update/history.xhtml",
           "Update:History",
@@ -2012,7 +2012,7 @@ function setupEventListeners() {
   }
   button = $("verify-place-integrity-button");
   if (button) {
-    button.addEventListener("click", function (event) {
+    button.addEventListener("click", function () {
       PlacesDBUtils.checkAndFixDatabase().then(tasksStatusMap => {
         let logs = [];
         for (let [key, value] of tasksStatusMap) {
@@ -2027,13 +2027,13 @@ function setupEventListeners() {
     });
   }
 
-  $("copy-raw-data-to-clipboard").addEventListener("click", function (event) {
+  $("copy-raw-data-to-clipboard").addEventListener("click", function () {
     copyRawDataToClipboard(this);
   });
-  $("copy-to-clipboard").addEventListener("click", function (event) {
+  $("copy-to-clipboard").addEventListener("click", function () {
     copyContentsToClipboard();
   });
-  $("profile-dir-button").addEventListener("click", function (event) {
+  $("profile-dir-button").addEventListener("click", function () {
     openProfileDirectory();
   });
 }
diff --git a/toolkit/content/aboutTelemetry.js b/toolkit/content/aboutTelemetry.js
index b25c2687d93d..45a848882042 100644
--- a/toolkit/content/aboutTelemetry.js
+++ b/toolkit/content/aboutTelemetry.js
@@ -257,7 +257,7 @@ var PingPicker = {
       "mouseleave",
       () => (pingPickerNeedHide = true)
     );
-    document.addEventListener("click", ev => {
+    document.addEventListener("click", () => {
       if (pingPickerNeedHide) {
         pingPicker.classList.add("hidden");
       }
@@ -966,7 +966,7 @@ var RawPayloadData = {
   attachObservers() {
     document
       .getElementById("payload-json-viewer")
-      .addEventListener("click", e => {
+      .addEventListener("click", () => {
         openJsonInFirefoxJsonViewer(JSON.stringify(gPingData.payload, null, 2));
       });
   },
@@ -1121,7 +1121,7 @@ var Histogram = {
     return outerDiv;
   },
 
-  processHistogram(aHgram, aName) {
+  processHistogram(aHgram) {
     const values = Object.keys(aHgram.values).map(k => aHgram.values[k]);
     if (!values.length) {
       // If we have no values collected for this histogram, just return
diff --git a/toolkit/content/aboutUrlClassifier.js b/toolkit/content/aboutUrlClassifier.js
index 14b34c7e8929..cc88e3bf73eb 100644
--- a/toolkit/content/aboutUrlClassifier.js
+++ b/toolkit/content/aboutUrlClassifier.js
@@ -429,7 +429,7 @@ var Cache = {
   createCacheEntries() {
     function createRow(tds, body, cols) {
       let tr = document.createElement("tr");
-      tds.forEach(function (v, i, a) {
+      tds.forEach(function (v, i) {
         let td = document.createElement("td");
         if (i == 0 && tds.length != cols) {
           td.setAttribute("colspan", cols - tds.length + 1);
diff --git a/toolkit/content/aboutwebrtc/aboutWebrtc.mjs b/toolkit/content/aboutwebrtc/aboutWebrtc.mjs
index 7e2c92a4bdf3..5aa8119c5ac4 100644
--- a/toolkit/content/aboutwebrtc/aboutWebrtc.mjs
+++ b/toolkit/content/aboutwebrtc/aboutWebrtc.mjs
@@ -53,7 +53,7 @@ class Renderer {
 // adding elements more readable, e.g. elemRenderer.elem_h4(...) instead of
 // elemRenderer.elem("h4", ...).
 const elemRenderer = new Proxy(new Renderer(), {
-  get(target, prop, receiver) {
+  get(target, prop) {
     // Function prefixes to proxy.
     const proxied = {
       elem_: (...args) => target.elem(...args),
@@ -502,7 +502,7 @@ async function renderPeerConnectionSection() {
       return body;
     },
     // Creates the filling for the disclosure
-    updateFn: async section => {
+    updateFn: async () => {
       let statsReports = await getStats(needsFullUpdate);
       needsFullUpdate = REQUEST_UPDATE_ONLY_REFRESH;
 
@@ -1828,7 +1828,7 @@ class PrimarySection {
     disclosureHideL10nId,
     autoRefreshPref,
     renderFn = async () => {}, // Creates the filling for the disclosure
-    updateFn = async section => {}, // Updates the contents.
+    updateFn = async () => {}, // Updates the contents.
     headerElementsFn = async () => [], // Accessory elements for the heading
   }) {
     const newSect = new PrimarySection();
@@ -1937,7 +1937,7 @@ async function renderMediaCtx(rndr) {
   hasH264Hardware.dataset.value = ctx.hasH264Hardware;
   const renderFn = async () =>
     rndr.elems_div({}, [hasH264Hardware, rndr.elem_hr(), confList.view()]);
-  const updateFn = async section => {
+  const updateFn = async () => {
     const newCtx = WGI.getMediaContext();
     if (hasH264Hardware.dataset.value != newCtx.hasH264Hardware) {
       hasH264Hardware.dataset.value = newCtx.hasH264Hardware;
diff --git a/toolkit/content/aboutwebrtc/graph.mjs b/toolkit/content/aboutwebrtc/graph.mjs
index f2c93f070980..002b3c9d2804 100644
--- a/toolkit/content/aboutwebrtc/graph.mjs
+++ b/toolkit/content/aboutwebrtc/graph.mjs
@@ -35,14 +35,14 @@ class GraphImpl {
   // The color to use for average graph lines and text
   averageLineColor = () => "green";
   // The color to use for the max value
-  maxColor = ({ time, value }) => "grey";
+  maxColor = () => "grey";
   // The color to use for the min value
-  minColor = ({ time, value }) => "grey";
+  minColor = () => "grey";
   // Title color
-  titleColor = title => compStyle("--in-content-page-color");
+  titleColor = () => compStyle("--in-content-page-color");
   // The color to use for a data point at a time.
   // The destination x coordinate and graph width are also provided.
-  datumColor = ({ time, value, x, width }) => "red";
+  datumColor = () => "red";
 
   // Returns an SVG element that needs to be inserted into the DOM for display
   drawSparseValues = (dataSet, title, config) => {
diff --git a/toolkit/content/contentAreaUtils.js b/toolkit/content/contentAreaUtils.js
index 983fd9890d84..0e7d072e6bed 100644
--- a/toolkit/content/contentAreaUtils.js
+++ b/toolkit/content/contentAreaUtils.js
@@ -1180,10 +1180,10 @@ function openURL(aURL) {
     var appstartup = Services.startup;
 
     var loadListener = {
-      onStartRequest: function ll_start(aRequest) {
+      onStartRequest: function ll_start() {
         appstartup.enterLastWindowClosingSurvivalArea();
       },
-      onStopRequest: function ll_stop(aRequest, aStatusCode) {
+      onStopRequest: function ll_stop() {
         appstartup.exitLastWindowClosingSurvivalArea();
       },
       QueryInterface: ChromeUtils.generateQI([
@@ -1194,13 +1194,13 @@ function openURL(aURL) {
     loadgroup.groupObserver = loadListener;
 
     var uriListener = {
-      doContent(ctype, preferred, request, handler) {
+      doContent() {
         return false;
       },
-      isPreferred(ctype, desired) {
+      isPreferred() {
         return false;
       },
-      canHandleContent(ctype, preferred, desired) {
+      canHandleContent() {
         return false;
       },
       loadCookie: null,
diff --git a/toolkit/content/tests/browser/browser_about_logging.js b/toolkit/content/tests/browser/browser_about_logging.js
index fdf8eab57bbb..d9a2459c12bb 100644
--- a/toolkit/content/tests/browser/browser_about_logging.js
+++ b/toolkit/content/tests/browser/browser_about_logging.js
@@ -201,7 +201,7 @@ add_task(async function testURLParameters() {
       url: PAGE + "?invalid-param",
     },
     async browser => {
-      await SpecialPowers.spawn(browser, [profilerPresetInURL], async inURL => {
+      await SpecialPowers.spawn(browser, [profilerPresetInURL], async () => {
         let $ = content.document.querySelector.bind(content.document);
         Assert.ok(
           !$("#error").hidden,
@@ -368,7 +368,7 @@ add_task(async function testProfilerOpens() {
       "https://example.com/",
       false
     );
-    SpecialPowers.spawn(browser, [], async savedLogModules => {
+    SpecialPowers.spawn(browser, [], async () => {
       let $ = content.document.querySelector.bind(content.document);
       // Override the URL the profiler uses to avoid hitting external
       // resources (and crash).
diff --git a/toolkit/content/tests/browser/browser_bug982298.js b/toolkit/content/tests/browser/browser_bug982298.js
index ffbc916a5e57..9b6f636db309 100644
--- a/toolkit/content/tests/browser/browser_bug982298.js
+++ b/toolkit/content/tests/browser/browser_bug982298.js
@@ -50,7 +50,7 @@ add_task(async function () {
 
       let awaitFindResult2 = new Promise(resolve => {
         let listener = {
-          onFindResult(aData) {
+          onFindResult() {
             info("got find result #2");
             browser.finder.removeResultListener(listener);
             resolve();
diff --git a/toolkit/content/tests/browser/browser_f7_caret_browsing.js b/toolkit/content/tests/browser/browser_f7_caret_browsing.js
index be6ae7d1f784..c0413c459bac 100644
--- a/toolkit/content/tests/browser/browser_f7_caret_browsing.js
+++ b/toolkit/content/tests/browser/browser_f7_caret_browsing.js
@@ -37,7 +37,7 @@ registerCleanupFunction(function () {
 let gCaretPromptOpeningObserver;
 function promiseCaretPromptOpened() {
   return new Promise(resolve => {
-    function observer(subject, topic, data) {
+    function observer(subject) {
       info("Dialog opened.");
       resolve(subject);
       gCaretPromptOpeningObserver();
diff --git a/toolkit/content/tests/browser/browser_isSynthetic.js b/toolkit/content/tests/browser/browser_isSynthetic.js
index 21b22fe1711e..3473dfc9157f 100644
--- a/toolkit/content/tests/browser/browser_isSynthetic.js
+++ b/toolkit/content/tests/browser/browser_isSynthetic.js
@@ -11,7 +11,7 @@ LocationChangeListener.prototype = {
     this.browser.removeProgressListener(this);
   },
 
-  onLocationChange(webProgress, request, location, flags) {
+  onLocationChange() {
     this.wasSynthetic = this.browser.isSyntheticDocument;
   },
 
diff --git a/toolkit/content/tests/browser/browser_media_wakelock_webaudio.js b/toolkit/content/tests/browser/browser_media_wakelock_webaudio.js
index 7c40b5fe1adc..9e18cc89f3ad 100644
--- a/toolkit/content/tests/browser/browser_media_wakelock_webaudio.js
+++ b/toolkit/content/tests/browser/browser_media_wakelock_webaudio.js
@@ -56,7 +56,6 @@ async function checkWakelockWhenChangeTabVisibility({
   description,
   additionalParams,
   needLock,
-  elementIdForEnteringPIPMode,
 }) {
   const originalTab = gBrowser.selectedTab;
   info(`start a new tab for '${description}'`);
diff --git a/toolkit/content/tests/browser/browser_save_folder_standalone_image.js b/toolkit/content/tests/browser/browser_save_folder_standalone_image.js
index 073e71a88b41..6bcc95ae654f 100644
--- a/toolkit/content/tests/browser/browser_save_folder_standalone_image.js
+++ b/toolkit/content/tests/browser/browser_save_folder_standalone_image.js
@@ -49,7 +49,7 @@ add_task(async function () {
   const IMAGE_URL =
     "http://mochi.test:8888/browser/toolkit/content/tests/browser/doggy.png";
 
-  await BrowserTestUtils.withNewTab(IMAGE_URL, async function (browser) {
+  await BrowserTestUtils.withNewTab(IMAGE_URL, async function () {
     let tmpDir = FileUtils.getDir("TmpD", []);
     let dir = newDirectory();
     let downloadLastDir = new DownloadLastDir(null);
diff --git a/toolkit/content/tests/browser/browser_save_resend_postdata.js b/toolkit/content/tests/browser/browser_save_resend_postdata.js
index 3f3e729dabc1..b028cac4ae55 100644
--- a/toolkit/content/tests/browser/browser_save_resend_postdata.js
+++ b/toolkit/content/tests/browser/browser_save_resend_postdata.js
@@ -59,7 +59,7 @@ function test() {
     var file = destDir.clone();
     file.append("no_default_file_name");
     MockFilePicker.setFiles([file]);
-    MockFilePicker.showCallback = function (fp) {
+    MockFilePicker.showCallback = function () {
       MockFilePicker.filterIndex = 1; // kSaveAsType_URL
     };
 
diff --git a/toolkit/content/tests/browser/common/mockTransfer.js b/toolkit/content/tests/browser/common/mockTransfer.js
index f4afa44903cf..0240d9c14b61 100644
--- a/toolkit/content/tests/browser/common/mockTransfer.js
+++ b/toolkit/content/tests/browser/common/mockTransfer.js
@@ -51,8 +51,7 @@ MockTransfer.prototype = {
   onStatusChange: function MTFC_onStatusChange(
     aWebProgress,
     aRequest,
-    aStatus,
-    aMessage
+    aStatus
   ) {
     // If at least one notification reported an error, the download failed.
     if (!Components.isSuccessCode(aStatus)) {
diff --git a/toolkit/content/tests/browser/datetime/head.js b/toolkit/content/tests/browser/datetime/head.js
index 46e2c78af57c..532f7743b260 100644
--- a/toolkit/content/tests/browser/datetime/head.js
+++ b/toolkit/content/tests/browser/datetime/head.js
@@ -69,7 +69,7 @@ class DateTimeTestHelper {
       [selector],
       async selector => {
         let input = content.document.querySelector(selector);
-        await ContentTaskUtils.waitForEvent(input, "change", false, e => {
+        await ContentTaskUtils.waitForEvent(input, "change", false, () => {
           ok(
             content.window.windowUtils.isHandlingUserInput,
             "isHandlingUserInput should be true"
diff --git a/toolkit/content/tests/browser/head.js b/toolkit/content/tests/browser/head.js
index be15cd968479..03a239463de9 100644
--- a/toolkit/content/tests/browser/head.js
+++ b/toolkit/content/tests/browser/head.js
@@ -177,7 +177,7 @@ function leave_icon(icon) {
  * Used to listen events if you just need it once
  */
 function once(target, name) {
-  var p = new Promise(function (resolve, reject) {
+  var p = new Promise(function (resolve) {
     target.addEventListener(
       name,
       function () {
diff --git a/toolkit/content/tests/chrome/bug263683_window.xhtml b/toolkit/content/tests/chrome/bug263683_window.xhtml
index b124361fd7eb..74846e3c2765 100644
--- a/toolkit/content/tests/chrome/bug263683_window.xhtml
+++ b/toolkit/content/tests/chrome/bug263683_window.xhtml
@@ -176,7 +176,7 @@
       const matches = JSON.parse(gFindBar._foundMatches.dataset.l10nArgs);
       is(matches.total, 2, "Found correct amount of matches")
 
-      await SpecialPowers.spawn(gBrowser, [], async function(args) {
+      await SpecialPowers.spawn(gBrowser, [], async function() {
         function getSelection(docShell) {
           let controller = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                                      .getInterface(Ci.nsISelectionDisplay)
diff --git a/toolkit/content/tests/chrome/bug366992_window.xhtml b/toolkit/content/tests/chrome/bug366992_window.xhtml
index 698d26b43ad1..ee595706f5c3 100644
--- a/toolkit/content/tests/chrome/bug366992_window.xhtml
+++ b/toolkit/content/tests/chrome/bug366992_window.xhtml
@@ -46,7 +46,7 @@
       isCommandEnabled(aCommand) {
         return aCommand == "cmd_delete";
       },
-      doCommand(aCommand) { }
+      doCommand() { }
     }
 
     function ok(condition, message) {
diff --git a/toolkit/content/tests/chrome/file_editor_with_autocomplete.js b/toolkit/content/tests/chrome/file_editor_with_autocomplete.js
index 78611efc702c..acf2c9e9df00 100644
--- a/toolkit/content/tests/chrome/file_editor_with_autocomplete.js
+++ b/toolkit/content/tests/chrome/file_editor_with_autocomplete.js
@@ -195,7 +195,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case: type 'Mo'",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("M", { shiftKey: true }, aWindow);
         synthesizeKey("o", {}, aWindow);
         return true;
@@ -212,7 +212,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case: select 'Mozilla' to complete the word",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("KEY_ArrowDown", {}, aWindow);
         synthesizeKey("KEY_Enter", {}, aWindow);
         return true;
@@ -226,7 +226,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case: undo the word, but typed text shouldn't be canceled",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -239,7 +239,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case: undo the typed text",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -252,7 +252,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case: redo the typed text",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -265,7 +265,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case: redo the word",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -278,7 +278,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case: removing all text for next test...",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("a", { accelKey: true }, aWindow);
         synthesizeKey("KEY_Backspace", {}, aWindow);
         return true;
@@ -293,7 +293,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case: type 'mo'",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("m", {}, aWindow);
         synthesizeKey("o", {}, aWindow);
         return true;
@@ -310,7 +310,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case: select 'Mozilla' to complete the word",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("KEY_ArrowDown", {}, aWindow);
         synthesizeKey("KEY_Enter", {}, aWindow);
         return true;
@@ -324,7 +324,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case: undo the word, but typed text shouldn't be canceled",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -337,7 +337,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case: undo the typed text",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -350,7 +350,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case: redo the typed text",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -363,7 +363,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case: redo the word",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -376,7 +376,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case: removing all text for next test...",
       completeDefaultIndex: false,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("a", { accelKey: true }, aWindow);
         synthesizeKey("KEY_Backspace", {}, aWindow);
         return true;
@@ -392,7 +392,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case (completeDefaultIndex is true): type 'Mo'",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("M", { shiftKey: true }, aWindow);
         synthesizeKey("o", {}, aWindow);
         return true;
@@ -410,7 +410,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case (completeDefaultIndex is true): select 'Mozilla' to complete the word",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("KEY_ArrowDown", {}, aWindow);
         synthesizeKey("KEY_Enter", {}, aWindow);
         return true;
@@ -424,7 +424,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case (completeDefaultIndex is true): undo the word, but typed text shouldn't be canceled",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -437,7 +437,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case (completeDefaultIndex is true): undo the typed text",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -450,7 +450,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case (completeDefaultIndex is true): redo the typed text",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -466,7 +466,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case (completeDefaultIndex is true): redo the word",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -479,7 +479,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text exactly matches the case (completeDefaultIndex is true): removing all text for next test...",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("a", { accelKey: true }, aWindow);
         synthesizeKey("KEY_Backspace", {}, aWindow);
         return true;
@@ -494,7 +494,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): type 'mo'",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("m", {}, aWindow);
         synthesizeKey("o", {}, aWindow);
         return true;
@@ -512,7 +512,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): select 'Mozilla' to complete the word",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("KEY_ArrowDown", {}, aWindow);
         synthesizeKey("KEY_Enter", {}, aWindow);
         return true;
@@ -528,7 +528,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): undo the selected word, but typed text shouldn't be canceled",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -541,7 +541,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): undo the word, but typed text shouldn't be canceled",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -554,7 +554,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): undo the typed text",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("z", { accelKey: true }, aWindow);
         return true;
       },
@@ -571,7 +571,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): redo the typed text",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -587,7 +587,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): redo the default index word",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -600,7 +600,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): redo the word",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("Z", { accelKey: true, shiftKey: true }, aWindow);
         return true;
       },
@@ -613,7 +613,7 @@ nsDoTestsForEditorWithAutoComplete.prototype = {
       description:
         "Undo/Redo behavior check when typed text does not match the case (completeDefaultIndex is true): removing all text for next test...",
       completeDefaultIndex: true,
-      execute(aWindow, aTarget) {
+      execute(aWindow) {
         synthesizeKey("a", { accelKey: true }, aWindow);
         synthesizeKey("KEY_Backspace", {}, aWindow);
         return true;
diff --git a/toolkit/content/tests/chrome/popup_trigger.js b/toolkit/content/tests/chrome/popup_trigger.js
index 003af044e536..71846a01ea52 100644
--- a/toolkit/content/tests/chrome/popup_trigger.js
+++ b/toolkit/content/tests/chrome/popup_trigger.js
@@ -238,7 +238,7 @@ var popupTests = [
       // rollup this way.
       // synthesizeMouse(gTrigger, 0, -12, { });
     },
-    result(testname, step) {
+    result(testname) {
       is(gMenuPopup.anchorNode, null, testname + " anchorNode");
       is(gMenuPopup.triggerNode, null, testname + " triggerNode");
       checkClosed("trigger", testname);
@@ -532,7 +532,7 @@ var popupTests = [
     // event to openPopup to check the trigger node.
     testname: "open popup anchored with override",
     events: ["popupshowing thepopup 0010", "popupshown thepopup"],
-    test(testname, step) {
+    test() {
       // attribute overrides the position passed in
       gMenuPopup.setAttribute("position", "end_after");
       gExpectedTriggerNode = gCachedEvent.target;
@@ -546,7 +546,7 @@ var popupTests = [
         gCachedEvent
       );
     },
-    result(testname, step) {
+    result(testname) {
       gExpectedTriggerNode = null;
       is(gMenuPopup.anchorNode, gTrigger, testname + " anchorNode");
       is(
@@ -564,7 +564,7 @@ var popupTests = [
       "popuphidden thepopup",
       "DOMMenuInactive thepopup",
     ],
-    test(testname, step) {
+    test(testname) {
       synthesizeKey("KEY_Escape");
       checkClosed("trigger", testname);
     },
@@ -574,12 +574,12 @@ var popupTests = [
     testname: "open popup anchored with offsets",
     events: ["popupshowing thepopup", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test() {
       // attribute is empty so does not override
       gMenuPopup.setAttribute("position", "");
       gMenuPopup.openPopup(gTrigger, "before_start", 5, 10, true, true);
     },
-    result(testname, step) {
+    result(testname) {
       compareEdge(gTrigger, gMenuPopup, "before_start", 5, 10, testname);
     },
   },
@@ -588,10 +588,10 @@ var popupTests = [
     // to the viewport.
     testname: "open popup unanchored",
     events: ["popupshowing thepopup", "popupshown thepopup"],
-    test(testname, step) {
+    test() {
       gMenuPopup.openPopup(null, "after_start", 6, 8, false);
     },
-    result(testname, step) {
+    result(testname) {
       var rect = gMenuPopup.getBoundingClientRect();
       ok(
         rect.left == 6 && rect.top == 8 && rect.right && rect.bottom,
@@ -607,11 +607,11 @@ var popupTests = [
       "popuphiding thepopup",
       "popuphidden thepopup",
     ],
-    test(testname, step) {
+    test() {
       var item3 = document.getElementById("item3");
       synthesizeMouse(item3, 4, 4, {});
     },
-    result(testname, step) {
+    result(testname) {
       checkClosed("trigger", testname);
     },
   },
@@ -625,18 +625,18 @@ var popupTests = [
       "popuphidden thepopup",
       "DOMMenuInactive thepopup",
     ],
-    test(testname, step) {
+    test() {
       gMenuPopup.hidePopup();
     },
   },
   {
     testname: "open popup at screen",
     events: ["popupshowing thepopup", "popupshown thepopup"],
-    test(testname, step) {
+    test() {
       gExpectedTriggerNode = "notset";
       gMenuPopup.openPopupAtScreen(gScreenX + 24, gScreenY + 20, false);
     },
-    result(testname, step) {
+    result(testname) {
       gExpectedTriggerNode = null;
       is(gMenuPopup.anchorNode, null, testname + " anchorNode");
       is(gMenuPopup.triggerNode, null, testname + " triggerNode");
@@ -670,7 +670,7 @@ var popupTests = [
   {
     testname: "open context popup at screen",
     events: ["popupshowing thepopup 0010", "popupshown thepopup"],
-    test(testname, step) {
+    test() {
       gExpectedTriggerNode = gCachedEvent.target;
       gMenuPopup.openPopupAtScreen(
         gScreenX + 8,
@@ -679,7 +679,7 @@ var popupTests = [
         gCachedEvent
       );
     },
-    result(testname, step) {
+    result(testname) {
       gExpectedTriggerNode = null;
       is(gMenuPopup.anchorNode, null, testname + " anchorNode");
       is(
@@ -873,7 +873,7 @@ var popupTests = [
     testname: "open context popup at screen with all modifiers set",
     events: ["popupshowing thepopup 1111", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test() {
       gMenuPopup.openPopupAtScreen(
         gScreenX + 8,
         gScreenY + 16,
@@ -885,10 +885,10 @@ var popupTests = [
   {
     testname: "open popup with open property",
     events: ["popupshowing thepopup", "popupshown thepopup"],
-    test(testname, step) {
+    test() {
       openMenu(gTrigger);
     },
-    result(testname, step) {
+    result(testname) {
       checkOpen("trigger", testname);
       if (gIsMenu) {
         compareEdge(gTrigger, gMenuPopup, "after_start", 0, 0, testname);
@@ -902,10 +902,10 @@ var popupTests = [
       "DOMMenuItemActive submenu",
       "popupshown submenupopup",
     ],
-    test(testname, step) {
+    test() {
       openMenu(document.getElementById("submenu"));
     },
-    result(testname, step) {
+    result(testname) {
       checkOpen("trigger", testname);
       checkOpen("submenu", testname);
       // XXXndeakin
@@ -929,17 +929,17 @@ var popupTests = [
     test() {
       gMenuPopup.hidePopup();
     },
-    result(testname, step) {
+    result(testname) {
       checkClosed("trigger", testname);
       checkClosed("submenu", testname);
     },
   },
   {
     testname: "open submenu with open property without parent open",
-    test(testname, step) {
+    test() {
       openMenu(document.getElementById("submenu"));
     },
-    result(testname, step) {
+    result(testname) {
       checkClosed("trigger", testname);
       checkClosed("submenu", testname);
     },
@@ -950,11 +950,11 @@ var popupTests = [
       return gIsMenu;
     },
     events: ["popupshowing thepopup", "popupshown thepopup"],
-    test(testname, step) {
+    test() {
       gMenuPopup.setAttribute("position", "before_start");
       openMenu(gTrigger);
     },
-    result(testname, step) {
+    result(testname) {
       compareEdge(gTrigger, gMenuPopup, "before_start", 0, 0, testname);
     },
   },
@@ -968,10 +968,10 @@ var popupTests = [
       "popuphidden thepopup",
       "DOMMenuInactive thepopup",
     ],
-    test(testname, step) {
+    test() {
       closeMenu(gTrigger, gMenuPopup);
     },
-    result(testname, step) {
+    result(testname) {
       checkClosed("trigger", testname);
     },
   },
@@ -982,13 +982,13 @@ var popupTests = [
     },
     events: ["popupshowing thepopup", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test() {
       gMenuPopup.setAttribute("position", "start_after");
       gMenuPopup.setAttribute("popupanchor", "topright");
       gMenuPopup.setAttribute("popupalign", "bottomright");
       openMenu(gTrigger);
     },
-    result(testname, step) {
+    result(testname) {
       compareEdge(gTrigger, gMenuPopup, "start_after", 0, 0, testname);
     },
   },
@@ -999,13 +999,13 @@ var popupTests = [
     },
     events: ["popupshowing thepopup", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test() {
       gMenuPopup.removeAttribute("position");
       gMenuPopup.setAttribute("popupanchor", "bottomright");
       gMenuPopup.setAttribute("popupalign", "topright");
       openMenu(gTrigger);
     },
-    result(testname, step) {
+    result(testname) {
       compareEdge(gTrigger, gMenuPopup, "after_end", 0, 0, testname);
       gMenuPopup.removeAttribute("popupanchor");
       gMenuPopup.removeAttribute("popupalign");
@@ -1018,11 +1018,11 @@ var popupTests = [
     },
     events: ["popupshowing thepopup", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test() {
       gTrigger.focus();
       synthesizeKey("KEY_ArrowDown", { altKey: !platformIsMac() });
     },
-    result(testname, step) {
+    result(testname) {
       checkOpen("trigger", testname);
       checkActive(gMenuPopup, "", testname);
     },
@@ -1033,11 +1033,11 @@ var popupTests = [
       return gIsMenu;
     },
     events: ["popupshowing thepopup", "popupshown thepopup"],
-    test(testname, step) {
+    test() {
       gTrigger.focus();
       synthesizeKey("KEY_ArrowUp", { altKey: !platformIsMac() });
     },
-    result(testname, step) {
+    result(testname) {
       checkOpen("trigger", testname);
       checkActive(gMenuPopup, "", testname);
     },
@@ -1055,11 +1055,11 @@ var popupTests = [
       "popuphiding thepopup",
       "popuphidden thepopup",
     ],
-    test(testname, step) {
+    test() {
       synthesizeKey("KEY_ArrowDown");
       synthesizeKey("KEY_Enter");
     },
-    result(testname, step) {
+    result(testname) {
       checkClosed("trigger", testname);
     },
   },
@@ -1070,11 +1070,11 @@ var popupTests = [
     },
     events: ["popupshowing thepopup", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test() {
       gTrigger.focus();
       synthesizeKey(platformIsMac() ? " " : "KEY_F4");
     },
-    result(testname, step) {
+    result(testname) {
       checkOpen("trigger", testname);
       checkActive(gMenuPopup, "", testname);
     },
@@ -1085,7 +1085,7 @@ var popupTests = [
     condition() {
       return gIsMenu;
     },
-    test(testname, step) {
+    test() {
       gTrigger.focus();
       if (platformIsMac()) {
         synthesizeKey("KEY_F4", { altKey: true });
@@ -1093,7 +1093,7 @@ var popupTests = [
         synthesizeKey("", { metaKey: true });
       }
     },
-    result(testname, step) {
+    result(testname) {
       checkClosed("trigger", testname);
     },
   },
@@ -1102,11 +1102,11 @@ var popupTests = [
     condition() {
       return gIsMenu;
     },
-    test(testname, step) {
+    test() {
       gTrigger.setAttribute("disabled", "true");
       synthesizeMouse(gTrigger, 4, 4, {});
     },
-    result(testname, step) {
+    result(testname) {
       checkClosed("trigger", testname);
       gTrigger.removeAttribute("disabled");
     },
@@ -1116,11 +1116,11 @@ var popupTests = [
     testname: "openPopup with object argument",
     events: ["popupshowing thepopup 0000", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test(testname) {
       gMenuPopup.openPopup(gTrigger, { position: "before_start", x: 5, y: 7 });
       checkOpen("trigger", testname);
     },
-    result(testname, step) {
+    result(testname) {
       var triggerrect = gTrigger.getBoundingClientRect();
       var popuprect = gMenuPopup.getBoundingClientRect();
       is(
@@ -1139,7 +1139,7 @@ var popupTests = [
     testname: "openPopup with object argument with event",
     events: ["popupshowing thepopup 1000", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test(testname) {
       gMenuPopup.openPopup(gTrigger, {
         position: "after_start",
         x: 0,
@@ -1153,10 +1153,10 @@ var popupTests = [
     testname: "openPopup with no arguments",
     events: ["popupshowing thepopup", "popupshown thepopup"],
     autohide: "thepopup",
-    test(testname, step) {
+    test() {
       gMenuPopup.openPopup();
     },
-    result(testname, step) {
+    result(testname) {
       let isMenu = gTrigger.type == "menu";
       // With no arguments, open in default menu position
       var triggerrect = gTrigger.getBoundingClientRect();
@@ -1184,7 +1184,7 @@ var popupTests = [
       "DOMMenuItemActive submenu",
       "popupshown submenupopup",
     ],
-    test(testname, step) {
+    test(testname) {
       gMenuPopup.openPopup(gTrigger, "after_start", 0, 0, false, true);
       document
         .getElementById("submenupopup")
@@ -1196,7 +1196,7 @@ var popupTests = [
   {
     // remove the content nodes for the popup
     testname: "remove content",
-    test(testname, step) {
+    test() {
       var submenupopup = document.getElementById("submenupopup");
       submenupopup.remove();
       var popup = document.getElementById("thepopup");
diff --git a/toolkit/content/tests/chrome/test_arrowpanel.xhtml b/toolkit/content/tests/chrome/test_arrowpanel.xhtml
index cd8d312e1d0d..f9f8a0eaf5fd 100644
--- a/toolkit/content/tests/chrome/test_arrowpanel.xhtml
+++ b/toolkit/content/tests/chrome/test_arrowpanel.xhtml
@@ -201,7 +201,7 @@ function* nextTest()
 
   // Test that a transition occurs when opening or closing the popup.
   if (matchMedia("(-moz-panel-animations").matches) {
-    function transitionEnded(event) {
+    function transitionEnded() {
       if ($("animatepanel").state != "open") {
         is($("animatepanel").state, "showing", "state is showing during transitionend");
         ok(!animatedPopupShown, "popupshown not fired yet")
diff --git a/toolkit/content/tests/chrome/test_menuitem_blink.xhtml b/toolkit/content/tests/chrome/test_menuitem_blink.xhtml
index 700a8a746553..ad76eee8bfa0 100644
--- a/toolkit/content/tests/chrome/test_menuitem_blink.xhtml
+++ b/toolkit/content/tests/chrome/test_menuitem_blink.xhtml
@@ -32,7 +32,7 @@ function test_crash() {
   var menupopup = document.getElementById("menupopup");
   var menuitem = document.getElementById("menuitem");
   menupopup.addEventListener("popupshown", function () {
-    menuitem.addEventListener("mouseup", function (e) {
+    menuitem.addEventListener("mouseup", function () {
       const observer = new MutationObserver((aMutationList, aObserver) => {
         for (const mutation of aMutationList) {
           if (mutation.attributeName != "_moz-menuactive") {
diff --git a/toolkit/content/tests/chrome/test_menulist_in_popup.xhtml b/toolkit/content/tests/chrome/test_menulist_in_popup.xhtml
index 971fe903223b..75fb19adcf15 100644
--- a/toolkit/content/tests/chrome/test_menulist_in_popup.xhtml
+++ b/toolkit/content/tests/chrome/test_menulist_in_popup.xhtml
@@ -17,7 +17,7 @@ async function runTest() {
   let menulist = document.getElementById("menulist");
   let menulistPopup = document.getElementById("menulistpopup");
 
-  menulistPopup.addEventListener("popupshown", function(e) {
+  menulistPopup.addEventListener("popupshown", function() {
     ok(false, "Menulist popup shown");
   });
 
diff --git a/toolkit/content/tests/chrome/test_notificationbox.xhtml b/toolkit/content/tests/chrome/test_notificationbox.xhtml
index 8de985175a29..9a2bc9d88838 100644
--- a/toolkit/content/tests/chrome/test_notificationbox.xhtml
+++ b/toolkit/content/tests/chrome/test_notificationbox.xhtml
@@ -89,8 +89,8 @@ function testtag_notificationbox_buttonpressed(notification, button)
 }
 
 let buttonsPressedLog = "";
-function testtag_notificationbox_button1pressed(notification, button) { buttonsPressedLog += "button1"; return true; }
-function testtag_notificationbox_button2pressed(notification, button) { buttonsPressedLog += "button2"; return true; }
+function testtag_notificationbox_button1pressed() { buttonsPressedLog += "button1"; return true; }
+function testtag_notificationbox_button2pressed() { buttonsPressedLog += "button2"; return true; }
 
 function testtag_notificationbox(nb)
 {
@@ -227,7 +227,7 @@ var tests =
       nb.removeNotification(ntf);
       return ntf;
     },
-    result(nb, ntf) {
+    result(nb) {
       testtag_notificationbox_State(nb, "removeNotification", null, 0);
     }
   },
@@ -394,7 +394,7 @@ var tests =
       nb.removeCurrentNotification();
       return ntf;
     },
-    result(nb, ntf) {
+    result(nb) {
       testtag_notificationbox_State(nb, "removeCurrentNotification", null, 0);
     }
   },
@@ -451,7 +451,7 @@ var tests =
         }, testtag_notificationbox_buttons_nopopup);
       return ntf;
     },
-    result(nb, ntf) {
+    result(nb) {
       let buttons = nb.currentNotification.buttonContainer.querySelectorAll("* button");
 
       buttons[0].focus();
@@ -510,7 +510,7 @@ var tests =
     }
   },
   {
-    async test(nb, unused) {
+    async test(nb) {
       // add a number of notifications and check that they are added in order
       await nb.appendNotification("4", { label: "Four", priority: nb.PRIORITY_INFO_HIGH },
                             testtag_notificationbox_buttons);
@@ -537,11 +537,11 @@ var tests =
   {
     // test closing notifications to make sure that the current notification is still set properly
     repeat: true,
-    test(nb, testidx) {
+    test() {
       this.repeat = false;
       return undefined;
     },
-    result(nb, arr) {
+    result(nb) {
         let notificationOrder = [4, 7, 2, 8, 5, 6, 1, 9, 10, 3];
         let allNotificationValues = [...nb.stack.children].map(n => n.getAttribute("value"));
         is(allNotificationValues.length, notificationOrder.length, "Expected number of notifications");
@@ -556,7 +556,7 @@ var tests =
     }
   },
   {
-    async test(nb, ntf) {
+    async test(nb) {
       var exh = false;
       try {
         await nb.appendNotification("no", { label: "no", priority: -1 });
diff --git a/toolkit/content/tests/chrome/test_popup_keys.xhtml b/toolkit/content/tests/chrome/test_popup_keys.xhtml
index 6b8dd3114302..e72c496a59d9 100644
--- a/toolkit/content/tests/chrome/test_popup_keys.xhtml
+++ b/toolkit/content/tests/chrome/test_popup_keys.xhtml
@@ -37,7 +37,7 @@ let gLastFirstMenuActiveValue = null;
 
 function waitForEvent(target, eventName) {
   return new Promise(resolve => {
-    target.addEventListener(eventName, function eventOccurred(event) {
+    target.addEventListener(eventName, function eventOccurred() {
       resolve();
     }, { once: true});
   });
diff --git a/toolkit/content/tests/chrome/test_popup_moveToAnchor.xhtml b/toolkit/content/tests/chrome/test_popup_moveToAnchor.xhtml
index a7800caaad50..628ff2a851a8 100644
--- a/toolkit/content/tests/chrome/test_popup_moveToAnchor.xhtml
+++ b/toolkit/content/tests/chrome/test_popup_moveToAnchor.xhtml
@@ -20,7 +20,7 @@
 <script>
 SimpleTest.waitForExplicitFinish();
 
-function runTest(id)
+function runTest()
 {
   $("popup").openPopup($("button1"), "after_start");
 }
diff --git a/toolkit/content/tests/chrome/test_tree_view.xhtml b/toolkit/content/tests/chrome/test_tree_view.xhtml
index 5e45161c6ce0..c9ec88999570 100644
--- a/toolkit/content/tests/chrome/test_tree_view.xhtml
+++ b/toolkit/content/tests/chrome/test_tree_view.xhtml
@@ -24,23 +24,23 @@ var view =
   value: "",
   rowCount: 8,
   getCellText(row, column) { return this.treeData[row % 4][column.index]; },
-  getCellValue(row, column) { return this.value; },
+  getCellValue() { return this.value; },
   setCellText(row, column, val) { this.treeData[row % 4][column.index] = val; },
   setCellValue(row, column, val) { this.value = val; },
   setTree(tree) { this.tree = tree; },
-  isContainer(row) { return false; },
-  isContainerOpen(row) { return false; },
-  isContainerEmpty(row) { return false; },
-  isSeparator(row) { return false; },
-  isSorted(row) { return false; },
+  isContainer() { return false; },
+  isContainerOpen() { return false; },
+  isContainerEmpty() { return false; },
+  isSeparator() { return false; },
+  isSorted() { return false; },
   isEditable(row, column) { return row != 2 || column.index != 1; },
-  getParentIndex(row, column) { return -1; },
-  getLevel(row) { return 0; },
-  hasNextSibling(row, column) { return row != this.rowCount - 1; },
-  getImageSrc(row, column) { return ""; },
-  cycleHeader(column) { },
-  getRowProperties(row) { return ""; },
-  getCellProperties(row, column) { return ""; },
+  getParentIndex() { return -1; },
+  getLevel() { return 0; },
+  hasNextSibling(row) { return row != this.rowCount - 1; },
+  getImageSrc() { return ""; },
+  cycleHeader() { },
+  getRowProperties() { return ""; },
+  getCellProperties() { return ""; },
   getColumnProperties(column)
   {
     if (!column.index) {
diff --git a/toolkit/content/tests/chrome/window_cursorsnap_dialog.xhtml b/toolkit/content/tests/chrome/window_cursorsnap_dialog.xhtml
index d5c0e2753eb9..fa239a87af15 100644
--- a/toolkit/content/tests/chrome/window_cursorsnap_dialog.xhtml
+++ b/toolkit/content/tests/chrome/window_cursorsnap_dialog.xhtml
@@ -60,7 +60,7 @@ function finish()
   window.close();
 }
 
-function onMouseMove(aEvent)
+function onMouseMove()
 {
   var button = document.getElementById("dialog").getButton("accept");
   if (button.disabled)
diff --git a/toolkit/content/tests/chrome/window_maximized_persist.xhtml b/toolkit/content/tests/chrome/window_maximized_persist.xhtml
index f7eb695f0f6b..10f7d36d0724 100644
--- a/toolkit/content/tests/chrome/window_maximized_persist.xhtml
+++ b/toolkit/content/tests/chrome/window_maximized_persist.xhtml
@@ -8,7 +8,7 @@
         id="window"
         persist="height width sizemode">
 <script type="application/javascript"><![CDATA[
-  window.addEventListener("sizemodechange", evt => {
+  window.addEventListener("sizemodechange", () => {
     window.arguments[0].postMessage("sizemodechange", "*");
   });
 ]]></script>
diff --git a/toolkit/content/tests/chrome/window_maximized_persist_with_no_titlebar.xhtml b/toolkit/content/tests/chrome/window_maximized_persist_with_no_titlebar.xhtml
index 83fede7faed3..e104dfa6525a 100644
--- a/toolkit/content/tests/chrome/window_maximized_persist_with_no_titlebar.xhtml
+++ b/toolkit/content/tests/chrome/window_maximized_persist_with_no_titlebar.xhtml
@@ -9,7 +9,7 @@
         id="window"
         persist="height width sizemode">
 <script type="application/javascript"><![CDATA[
-  window.addEventListener("sizemodechange", evt => {
+  window.addEventListener("sizemodechange", () => {
     window.arguments[0].postMessage("sizemodechange", "*");
   });
 ]]></script>
diff --git a/toolkit/content/tests/chrome/window_popup_anchoratrect.xhtml b/toolkit/content/tests/chrome/window_popup_anchoratrect.xhtml
index 524a95b643f3..2262ba08e9bf 100644
--- a/toolkit/content/tests/chrome/window_popup_anchoratrect.xhtml
+++ b/toolkit/content/tests/chrome/window_popup_anchoratrect.xhtml
@@ -79,7 +79,7 @@ let tests = [
   },
 ];
 
-function runTest(id)
+function runTest()
 {
   menupopup = $("popup");
   nextTest();
diff --git a/toolkit/content/tests/widgets/head.js b/toolkit/content/tests/widgets/head.js
index d7473fa92dfd..2a72845a2741 100644
--- a/toolkit/content/tests/widgets/head.js
+++ b/toolkit/content/tests/widgets/head.js
@@ -51,7 +51,7 @@ function executeTests() {
 }
 
 function once(target, name, cb) {
-  let p = new Promise(function (resolve, reject) {
+  let p = new Promise(function (resolve) {
     target.addEventListener(
       name,
       function () {
diff --git a/toolkit/content/tests/widgets/test_moz_card.html b/toolkit/content/tests/widgets/test_moz_card.html
index ef4e67d0faac..06b8b463c733 100644
--- a/toolkit/content/tests/widgets/test_moz_card.html
+++ b/toolkit/content/tests/widgets/test_moz_card.html
@@ -58,7 +58,7 @@
 
     }
 
-    function assertAccordionCardProperties(card, expectedValues) {
+    function assertAccordionCardProperties(card) {
       ok(card.detailsEl, "The details element should exist");
       ok(card.detailsEl.querySelector("summary"), "There should be a summary element within the details element");
       ok(card.detailsEl.querySelector("summary").querySelector(".chevron-icon"), "There should be a chevron icon div within the summary element");
diff --git a/toolkit/content/tests/widgets/test_popupreflows.xhtml b/toolkit/content/tests/widgets/test_popupreflows.xhtml
index c3f80687791c..c014d6bee4d0 100644
--- a/toolkit/content/tests/widgets/test_popupreflows.xhtml
+++ b/toolkit/content/tests/widgets/test_popupreflows.xhtml
@@ -20,7 +20,7 @@ let panel, anchor;
 // done by the panel.
 let observer = {
   reflows: [],
-  reflow (start, end) {
+  reflow () {
     // Ignore reflows triggered by native code
     // (Reflows from native code only have an empty stack after the first frame)
     var path = (new Error().stack).split("\n").slice(1).join("");
@@ -31,7 +31,7 @@ let observer = {
     this.reflows.push(new Error().stack);
   },
 
-  reflowInterruptible (start, end) {
+  reflowInterruptible () {
     // We're not interested in interruptible reflows.  Why, you ask?  Because
     // we've simply cargo-culted this test from browser_tabopen_reflows.js!
   },
diff --git a/toolkit/content/tests/widgets/test_videocontrols.html b/toolkit/content/tests/widgets/test_videocontrols.html
index 076b4350fd91..35678fa05ef5 100644
--- a/toolkit/content/tests/widgets/test_videocontrols.html
+++ b/toolkit/content/tests/widgets/test_videocontrols.html
@@ -437,7 +437,7 @@ add_task(async function click_and_hold_slider() {
  * Bug 1402877: Don't let click event dispatch through media controls to video element.
  */
 add_task(async function click_event_dispatch() {
-  const clientScriptClickHandler = (e) => {
+  const clientScriptClickHandler = () => {
     ok(false, "Should not receive the event");
   };
   video.addEventListener("click", clientScriptClickHandler);
diff --git a/toolkit/content/tests/widgets/test_videocontrols_audio.html b/toolkit/content/tests/widgets/test_videocontrols_audio.html
index ad528f4c2794..0a7a2dcbc3cc 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_audio.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_audio.html
@@ -18,7 +18,7 @@
 <script>
 
   const video = document.getElementById("video");
-  function loadedmetadata(event) {
+  function loadedmetadata() {
     SimpleTest.executeSoon(function() {
       const controlBar = SpecialPowers.wrap(video).openOrClosedShadowRoot.querySelector(".controlBar");
       is(controlBar.getAttribute("fullscreen-unavailable"), "true", "Fullscreen button is hidden");
diff --git a/toolkit/content/tests/widgets/test_videocontrols_jsdisabled.html b/toolkit/content/tests/widgets/test_videocontrols_jsdisabled.html
index f3fdecc47f06..16cf2b92e057 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_jsdisabled.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_jsdisabled.html
@@ -45,7 +45,7 @@ SpecialPowers.pushPrefEnv({"set": [["javascript.enabled", false]]}, startTest);
 var testnum = 1;
 
 var video;
-function loadevent(event) {
+function loadevent() {
   is(win.testExpando, undefined, "expando shouldn't exist because js is disabled");
   video = win.document.querySelector("video");
   // Other events expected by the test.
diff --git a/toolkit/content/tests/widgets/test_videocontrols_onclickplay.html b/toolkit/content/tests/widgets/test_videocontrols_onclickplay.html
index 9023512ab70d..6af2df6d9183 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_onclickplay.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_onclickplay.html
@@ -26,7 +26,7 @@ function startMediaLoad() {
   video.addEventListener("canplaythrough", runTest);
 }
 
-function loadevent(event) {
+function loadevent() {
   SpecialPowers.pushPrefEnv({"set": [["media.cache_size", 40000]]}, startMediaLoad);
 }
 
diff --git a/toolkit/content/tests/widgets/tree_shared.js b/toolkit/content/tests/widgets/tree_shared.js
index ed3c4797fa3b..2cc40686ec23 100644
--- a/toolkit/content/tests/widgets/tree_shared.js
+++ b/toolkit/content/tests/widgets/tree_shared.js
@@ -570,10 +570,10 @@ function testtag_tree_TreeSelection_UI(tree, testid, multiple) {
 
   var keydownFired = 0;
   var keypressFired = 0;
-  function keydownListener(event) {
+  function keydownListener() {
     keydownFired++;
   }
-  function keypressListener(event) {
+  function keypressListener() {
     keypressFired++;
   }
 
@@ -1303,7 +1303,7 @@ function testtag_tree_TreeView_rows(tree, testid, rowInfo, startRow) {
     isContainer(row) {
       return row.container;
     },
-    isContainerOpen(row) {
+    isContainerOpen() {
       return false;
     },
     isContainerEmpty(row) {
@@ -1321,7 +1321,7 @@ function testtag_tree_TreeView_rows(tree, testid, rowInfo, startRow) {
     getParentIndex(row) {
       return row.parent;
     },
-    hasNextSibling(row) {
+    hasNextSibling() {
       return r < startRow + length - 1;
     },
   };
@@ -1429,7 +1429,7 @@ function testtag_tree_TreeView_rows(tree, testid, rowInfo, startRow) {
   }
 }
 
-function testtag_tree_TreeView_rows_sort(tree, testid, rowInfo) {
+function testtag_tree_TreeView_rows_sort(tree) {
   // check if cycleHeader sorts the columns
   var columnIndex = 0;
   var view = tree.view;
@@ -1730,7 +1730,7 @@ function testtag_tree_wheel(aTree) {
 
   var defaultPrevented = 0;
 
-  function wheelListener(event) {
+  function wheelListener() {
     defaultPrevented++;
   }
   window.addEventListener("wheel", wheelListener);
@@ -2105,7 +2105,7 @@ function mouseClickOnColumnHeader(
   }
 }
 
-function mouseDblClickOnCell(tree, row, column, testname) {
+function mouseDblClickOnCell(tree, row, column) {
   // select the row we will edit
   var selection = tree.view.selection;
   selection.select(row);
diff --git a/toolkit/content/tests/widgets/videocontrols_direction_test.js b/toolkit/content/tests/widgets/videocontrols_direction_test.js
index e937f06b3fb9..608a39cc5b39 100644
--- a/toolkit/content/tests/widgets/videocontrols_direction_test.js
+++ b/toolkit/content/tests/widgets/videocontrols_direction_test.js
@@ -26,7 +26,7 @@ RemoteCanvas.prototype.load = function (callback) {
     var m = iframe.contentDocument.getElementById("av");
     m.addEventListener(
       "suspend",
-      function (aEvent) {
+      function () {
         setTimeout(function () {
           let mediaElement =
             iframe.contentDocument.querySelector("audio, video");
diff --git a/toolkit/content/tests/widgets/window_menubar.xhtml b/toolkit/content/tests/widgets/window_menubar.xhtml
index c4ced844adc8..ded1361365ec 100644
--- a/toolkit/content/tests/widgets/window_menubar.xhtml
+++ b/toolkit/content/tests/widgets/window_menubar.xhtml
@@ -426,7 +426,7 @@ var popupTests = [
   test() {
     synthesizeKey("KEY_Escape");
   },
-  result(testname) {
+  result() {
   },
 },
 {
@@ -504,14 +504,14 @@ var popupTests = [
   testname: "cursor up wrap",
   events: [ "DOMMenuItemInactive contents", "DOMMenuItemActive about" ],
   test() { synthesizeKey("KEY_ArrowUp"); },
-  result(testname) { }
+  result() { }
 },
 {
   // check that pressing cursor down skips non menuitems
   testname: "cursor down wrap",
   events: [ "DOMMenuItemInactive about", "DOMMenuItemActive contents" ],
   test() { synthesizeKey("KEY_ArrowDown"); },
-  result(testname) { }
+  result() { }
 },
 {
   // check that pressing a menuitem's accelerator selects it
@@ -617,7 +617,7 @@ var popupTests = [
   condition() { return kIsWindows; },
   events: [ "DOMMenuItemInactive only", "DOMMenuItemActive other" ],
   test() { sendChar("o"); },
-  result(testname) { }
+  result() { }
 },
 {
   // when only one menuitem starting with that letter exists, it should be
diff --git a/toolkit/crashreporter/CrashSubmit.sys.mjs b/toolkit/crashreporter/CrashSubmit.sys.mjs
index 28647c5a83ca..dd40fea9468e 100644
--- a/toolkit/crashreporter/CrashSubmit.sys.mjs
+++ b/toolkit/crashreporter/CrashSubmit.sys.mjs
@@ -259,7 +259,7 @@ Submitter.prototype = {
     let manager = Services.crashmanager;
     let submissionID = manager.generateSubmissionID();
 
-    xhr.addEventListener("readystatechange", evt => {
+    xhr.addEventListener("readystatechange", () => {
       if (xhr.readyState == 4) {
         let ret =
           xhr.status === 200 ? this.parseResponse(xhr.responseText) : {};
diff --git a/toolkit/crashreporter/test/unit/test_crash_stack_overflow.js b/toolkit/crashreporter/test/unit/test_crash_stack_overflow.js
index a47c2172382e..7c1d3821ec2a 100644
--- a/toolkit/crashreporter/test/unit/test_crash_stack_overflow.js
+++ b/toolkit/crashreporter/test/unit/test_crash_stack_overflow.js
@@ -12,7 +12,7 @@ add_task(async function run_test() {
       crashType = CrashTestUtils.CRASH_STACK_OVERFLOW;
       crashReporter.annotateCrashReport("TestKey", "TestValue");
     },
-    async function (mdump, extra, extraFile) {
+    async function (mdump, extra) {
       Assert.equal(extra.TestKey, "TestValue");
     },
     // process will exit with a zero exit status
diff --git a/toolkit/crashreporter/test/unit/test_crashreporter_appmem.js b/toolkit/crashreporter/test/unit/test_crashreporter_appmem.js
index f42fe10f0cb7..dcf5bd315392 100644
--- a/toolkit/crashreporter/test/unit/test_crashreporter_appmem.js
+++ b/toolkit/crashreporter/test/unit/test_crashreporter_appmem.js
@@ -4,7 +4,7 @@ add_task(async function run_test() {
       let appAddr = CrashTestUtils.saveAppMemory();
       crashReporter.registerAppMemory(appAddr, 32);
     },
-    function (mdump, extra) {
+    function (mdump) {
       Assert.ok(mdump.exists());
       Assert.ok(mdump.fileSize > 0);
       Assert.ok(CrashTestUtils.dumpCheckMemory(mdump.path));
diff --git a/toolkit/crashreporter/test/unit/test_event_files.js b/toolkit/crashreporter/test/unit/test_event_files.js
index 844d7700fff6..f4054089ea37 100644
--- a/toolkit/crashreporter/test/unit/test_event_files.js
+++ b/toolkit/crashreporter/test/unit/test_event_files.js
@@ -24,7 +24,7 @@ add_task(async function test_main_process_crash() {
         crashType = CrashTestUtils.CRASH_MOZ_CRASH;
         crashReporter.annotateCrashReport("ShutdownProgress", "event-test");
       },
-      (minidump, extra) => {
+      minidump => {
         basename = minidump.leafName;
         Object.defineProperty(cm, "_eventsDirs", { value: [getEventDir()] });
         cm.aggregateEventsFiles().then(resolve, reject);
diff --git a/toolkit/crashreporter/test/unit/test_override_exception_handler.js b/toolkit/crashreporter/test/unit/test_override_exception_handler.js
index 1b4dec8a61aa..caabc12de844 100644
--- a/toolkit/crashreporter/test/unit/test_override_exception_handler.js
+++ b/toolkit/crashreporter/test/unit/test_override_exception_handler.js
@@ -5,7 +5,7 @@ add_task(async function run_test() {
     function () {
       CrashTestUtils.TryOverrideExceptionHandler();
     },
-    function (mdump, extra) {},
+    function () {},
     true
   );
 });
diff --git a/toolkit/crashreporter/test/unit_ipc/test_content_memory_list.js b/toolkit/crashreporter/test/unit_ipc/test_content_memory_list.js
index 733d224160e4..b3770c7bcc33 100644
--- a/toolkit/crashreporter/test/unit_ipc/test_content_memory_list.js
+++ b/toolkit/crashreporter/test/unit_ipc/test_content_memory_list.js
@@ -18,7 +18,7 @@ add_task(async function run_test() {
     is_win7_or_newer = true;
   }
 
-  await do_content_crash(null, function (mdump, extra) {
+  await do_content_crash(null, function (mdump) {
     Assert.ok(mdump.exists());
     Assert.ok(mdump.fileSize > 0);
     if (is_win7_or_newer) {
diff --git a/toolkit/modules/AppMenuNotifications.sys.mjs b/toolkit/modules/AppMenuNotifications.sys.mjs
index 77487437ac7a..3e148f6e21b1 100644
--- a/toolkit/modules/AppMenuNotifications.sys.mjs
+++ b/toolkit/modules/AppMenuNotifications.sys.mjs
@@ -30,7 +30,7 @@ export var AppMenuNotifications = {
     Services.obs.removeObserver(this, "appMenu-notifications-request");
   },
 
-  observe(subject, topic, status) {
+  observe(subject, topic) {
     switch (topic) {
       case "xpcom-shutdown":
         this.uninit();
diff --git a/toolkit/modules/AsanReporter.sys.mjs b/toolkit/modules/AsanReporter.sys.mjs
index 172e24ca4bd6..3e24ae8a9695 100644
--- a/toolkit/modules/AsanReporter.sys.mjs
+++ b/toolkit/modules/AsanReporter.sys.mjs
@@ -56,7 +56,7 @@ export const AsanReporter = {
     processDirectory();
   },
 
-  observe(aSubject, aTopic, aData) {
+  observe(aSubject, aTopic) {
     if (aTopic == "ipc:content-shutdown") {
       aSubject.QueryInterface(Ci.nsIPropertyBag2);
       if (!aSubject.get("abnormal")) {
diff --git a/toolkit/modules/AsyncPrefs.sys.mjs b/toolkit/modules/AsyncPrefs.sys.mjs
index 5fa0ea6d6f9e..61075cc419be 100644
--- a/toolkit/modules/AsyncPrefs.sys.mjs
+++ b/toolkit/modules/AsyncPrefs.sys.mjs
@@ -103,7 +103,7 @@ export var AsyncPrefs = {
     return AsyncPrefsParent.set(pref, value);
   },
 
-  reset(pref, value) {
+  reset(pref) {
     if (kInChildProcess) {
       return ChromeUtils.domProcessChild.getActor("AsyncPrefs").reset(pref);
     }
diff --git a/toolkit/modules/FindBarContent.sys.mjs b/toolkit/modules/FindBarContent.sys.mjs
index ef3a197d5068..cdeead2a6eba 100644
--- a/toolkit/modules/FindBarContent.sys.mjs
+++ b/toolkit/modules/FindBarContent.sys.mjs
@@ -20,7 +20,7 @@ export class FindBarContent {
     this.addedEventListener = false;
   }
 
-  start(event) {
+  start() {
     this.inPassThrough = true;
   }
 
@@ -100,7 +100,7 @@ export class FindBarContent {
     this.actor.sendAsyncMessage("Findbar:Keypress", fakeEvent);
   }
 
-  onMouseup(event) {
+  onMouseup() {
     if (this.findMode != FIND_NORMAL) {
       this.actor.sendAsyncMessage("Findbar:Mouseup", {});
     }
diff --git a/toolkit/modules/Finder.sys.mjs b/toolkit/modules/Finder.sys.mjs
index 0b54b2caad45..f5d0452e39b0 100644
--- a/toolkit/modules/Finder.sys.mjs
+++ b/toolkit/modules/Finder.sys.mjs
@@ -100,7 +100,7 @@ Finder.prototype = {
     this._listeners = this._listeners.filter(l => l != aListener);
   },
 
-  _setResults(options, mode) {
+  _setResults(options) {
     if (typeof options.storeResult != "boolean") {
       options.storeResult = true;
     }
diff --git a/toolkit/modules/FinderHighlighter.sys.mjs b/toolkit/modules/FinderHighlighter.sys.mjs
index 2ebf718bd0b2..655792e49809 100644
--- a/toolkit/modules/FinderHighlighter.sys.mjs
+++ b/toolkit/modules/FinderHighlighter.sys.mjs
@@ -146,7 +146,7 @@ function mockAnonymousContentNode(domNode) {
         duration
       );
     },
-    setCutoutRectsForElement(id, rects) {
+    setCutoutRectsForElement() {
       // no-op for now.
     },
   };
@@ -217,7 +217,7 @@ FinderHighlighter.prototype = {
    * @param  {nsIDOMWindow} window
    * @return {Object}
    */
-  getForWindow(window, propName = null) {
+  getForWindow(window) {
     if (!gWindows.has(window)) {
       gWindows.set(window, {
         detectedGeometryChange: false,
@@ -661,7 +661,7 @@ FinderHighlighter.prototype = {
       this.setScrollMarks(window, Array.from(marks), onHorizontalScrollbar);
 
       if (!this._marksListener) {
-        this._marksListener = event => {
+        this._marksListener = () => {
           this.updateScrollMarks();
         };
 
@@ -1966,7 +1966,7 @@ FinderHighlighter.prototype = {
 
   // Start of nsIEditActionListener implementations
 
-  WillDeleteText(textNode, offset, length) {
+  WillDeleteText(textNode, offset) {
     let editor = this._getEditableNode(textNode).editor;
     let controller = editor.selectionController;
     let fSelection = controller.getSelection(
@@ -2131,7 +2131,7 @@ FinderHighlighter.prototype = {
       },
 
       // Unimplemented
-      notifyDocumentStateChanged(aDirty) {},
+      notifyDocumentStateChanged() {},
     };
   },
 };
diff --git a/toolkit/modules/FinderParent.sys.mjs b/toolkit/modules/FinderParent.sys.mjs
index 8c8437f5e98a..1f66ec95b0da 100644
--- a/toolkit/modules/FinderParent.sys.mjs
+++ b/toolkit/modules/FinderParent.sys.mjs
@@ -143,7 +143,7 @@ FinderParent.prototype = {
       let actor = windowGlobal.getActor("Finder");
       return actor.sendQuery(aMessageName, aArgs).then(
         result => result,
-        r => {}
+        () => {}
       );
     }
 
diff --git a/toolkit/modules/GMPInstallManager.sys.mjs b/toolkit/modules/GMPInstallManager.sys.mjs
index 41f57b9a6388..f56d0c742fe5 100644
--- a/toolkit/modules/GMPInstallManager.sys.mjs
+++ b/toolkit/modules/GMPInstallManager.sys.mjs
@@ -55,7 +55,7 @@ function downloadJSON(uri) {
   return new Promise((resolve, reject) => {
     let xmlHttp = new lazy.ServiceRequest({ mozAnon: true });
 
-    xmlHttp.onload = function (aResponse) {
+    xmlHttp.onload = function () {
       resolve(JSON.parse(this.responseText));
     };
 
diff --git a/toolkit/modules/HiddenFrame.sys.mjs b/toolkit/modules/HiddenFrame.sys.mjs
index 23ad57c0d3a3..74fe755796b2 100644
--- a/toolkit/modules/HiddenFrame.sys.mjs
+++ b/toolkit/modules/HiddenFrame.sys.mjs
@@ -89,7 +89,7 @@ HiddenFrame.prototype = {
         "nsISupportsWeakReference",
       ]),
     };
-    this._listener.onStateChange = (wbp, request, stateFlags, status) => {
+    this._listener.onStateChange = (wbp, request, stateFlags) => {
       if (!request) {
         return;
       }
diff --git a/toolkit/modules/LightweightThemeConsumer.sys.mjs b/toolkit/modules/LightweightThemeConsumer.sys.mjs
index cf388eb3d393..88a6d05aa9ea 100644
--- a/toolkit/modules/LightweightThemeConsumer.sys.mjs
+++ b/toolkit/modules/LightweightThemeConsumer.sys.mjs
@@ -30,7 +30,7 @@ const toolkitVariableMap = [
     "--lwt-accent-color",
     {
       lwtProperty: "accentcolor",
-      processColor(rgbaChannels, element) {
+      processColor(rgbaChannels) {
         if (!rgbaChannels || rgbaChannels.a == 0) {
           return "white";
         }
@@ -44,7 +44,7 @@ const toolkitVariableMap = [
     "--lwt-text-color",
     {
       lwtProperty: "textcolor",
-      processColor(rgbaChannels, element) {
+      processColor(rgbaChannels) {
         if (!rgbaChannels) {
           rgbaChannels = { r: 0, g: 0, b: 0 };
         }
@@ -147,7 +147,7 @@ const toolkitVariableMap = [
     "--lwt-toolbar-field-highlight",
     {
       lwtProperty: "toolbar_field_highlight",
-      processColor(rgbaChannels, element) {
+      processColor(rgbaChannels) {
         if (!rgbaChannels) {
           return null;
         }
@@ -207,7 +207,7 @@ export function LightweightThemeConsumer(aDocument) {
 LightweightThemeConsumer.prototype = {
   _lastData: null,
 
-  observe(aSubject, aTopic, aData) {
+  observe(aSubject, aTopic) {
     if (aTopic != "lightweight-theme-styling-update") {
       return;
     }
diff --git a/toolkit/modules/NewTabUtils.sys.mjs b/toolkit/modules/NewTabUtils.sys.mjs
index 00067ada122c..4fb4c7f91213 100644
--- a/toolkit/modules/NewTabUtils.sys.mjs
+++ b/toolkit/modules/NewTabUtils.sys.mjs
@@ -602,12 +602,12 @@ var PlacesProvider = {
         }
       },
 
-      handleError(aError) {
+      handleError() {
         // Should we somehow handle this error?
         aCallback([]);
       },
 
-      handleCompletion(aReason) {
+      handleCompletion() {
         // The Places query breaks ties in frecency by place ID descending, but
         // that's different from how Links.compareLinks breaks ties, because
         // compareLinks doesn't have access to place IDs.  It's very important
@@ -2101,7 +2101,7 @@ var Links = {
    * Implements the nsIObserver interface to get notified about browser history
    * sanitization.
    */
-  observe: function Links_observe(aSubject, aTopic, aData) {
+  observe: function Links_observe() {
     // Make sure to update open about:newtab instances. If there are no opened
     // pages we can just wait for the next new tab to populate the cache again.
     if (AllPages.length && AllPages.enabled) {
@@ -2182,7 +2182,7 @@ var Telemetry = {
   /**
    * Listens for gather telemetry topic.
    */
-  observe: function Telemetry_observe(aSubject, aTopic, aData) {
+  observe: function Telemetry_observe() {
     this._collect();
   },
 };
diff --git a/toolkit/modules/PopupNotifications.sys.mjs b/toolkit/modules/PopupNotifications.sys.mjs
index 2f4893a2f6a9..cbc531949877 100644
--- a/toolkit/modules/PopupNotifications.sys.mjs
+++ b/toolkit/modules/PopupNotifications.sys.mjs
@@ -689,7 +689,7 @@ PopupNotifications.prototype = {
    */
   suppressWhileOpen(panel) {
     this._hidePanel().catch(console.error);
-    panel.addEventListener("popuphidden", aEvent => {
+    panel.addEventListener("popuphidden", () => {
       this._update();
     });
   },
@@ -1369,7 +1369,7 @@ PopupNotifications.prototype = {
           true
         );
       }
-      this._popupshownListener = function (e) {
+      this._popupshownListener = function () {
         target.removeEventListener(
           "popupshown",
           this._popupshownListener,
diff --git a/toolkit/modules/Region.sys.mjs b/toolkit/modules/Region.sys.mjs
index a07e73f378f8..559273461fd3 100644
--- a/toolkit/modules/Region.sys.mjs
+++ b/toolkit/modules/Region.sys.mjs
@@ -843,7 +843,7 @@ class RegionDetector {
     }
   }
 
-  observe(aSubject, aTopic, aData) {
+  observe(aSubject, aTopic) {
     log.info(`Observed ${aTopic}`);
     switch (aTopic) {
       case GEOLOCATION_TOPIC:
diff --git a/toolkit/modules/UpdateUtils.sys.mjs b/toolkit/modules/UpdateUtils.sys.mjs
index 01149dbae334..be9ce9d5402c 100644
--- a/toolkit/modules/UpdateUtils.sys.mjs
+++ b/toolkit/modules/UpdateUtils.sys.mjs
@@ -269,7 +269,7 @@ export var UpdateUtils = {
           initialConfig[prefName] = initialValue;
         } catch (e) {}
 
-        Services.prefs.addObserver(prefName, async (subject, topic, data) => {
+        Services.prefs.addObserver(prefName, async () => {
           let config = { ...gUpdateConfigCache };
           config[prefName] = await UpdateUtils.readUpdateConfigSetting(
             prefName
diff --git a/toolkit/modules/tests/browser/browser_Finder.js b/toolkit/modules/tests/browser/browser_Finder.js
index 7bcf7e8a00a8..03724d2548b5 100644
--- a/toolkit/modules/tests/browser/browser_Finder.js
+++ b/toolkit/modules/tests/browser/browser_Finder.js
@@ -44,7 +44,7 @@ add_task(async function () {
   findResult = await promiseFind;
   is(findResult.result, Ci.nsITypeAheadFind.FIND_FOUND, "should find link");
 
-  await SpecialPowers.spawn(tab.linkedBrowser, [], async function (arg) {
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async function () {
     Assert.ok(
       !!content.document.getElementsByTagName("a")[0].style.outline,
       "outline set"
@@ -61,7 +61,7 @@ add_task(async function () {
     "should find link again"
   );
 
-  await SpecialPowers.spawn(tab.linkedBrowser, [], async function (arg) {
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async function () {
     Assert.ok(
       !content.document.getElementsByTagName("a")[0].style.outline,
       "outline not set"
diff --git a/toolkit/modules/tests/browser/browser_FinderHighlighter.js b/toolkit/modules/tests/browser/browser_FinderHighlighter.js
index 7e377e47d13b..be4f0fefef38 100644
--- a/toolkit/modules/tests/browser/browser_FinderHighlighter.js
+++ b/toolkit/modules/tests/browser/browser_FinderHighlighter.js
@@ -33,7 +33,7 @@ add_task(async function testModalResults() {
         insertCalls: [5, 6],
         removeCalls: [4, 5],
         // eslint-disable-next-line object-shorthand
-        extraTest: function (maskNode, outlineNode, rects) {
+        extraTest: function (maskNode, outlineNode) {
           Assert.equal(
             outlineNode.getElementsByTagName("div").length,
             2,
diff --git a/toolkit/modules/tests/browser/browser_Troubleshoot.js b/toolkit/modules/tests/browser/browser_Troubleshoot.js
index d627f175e458..b99a1fe3e0ca 100644
--- a/toolkit/modules/tests/browser/browser_Troubleshoot.js
+++ b/toolkit/modules/tests/browser/browser_Troubleshoot.js
@@ -1346,9 +1346,9 @@ function validateObject_array(array, schema) {
   array.forEach(elt => validateObject(elt, schema.items));
 }
 
-function validateObject_string(str, schema) {}
-function validateObject_boolean(bool, schema) {}
-function validateObject_number(num, schema) {}
+function validateObject_string() {}
+function validateObject_boolean() {}
+function validateObject_number() {}
 
 function validationErr(msg, obj, schema) {
   return new Error(
diff --git a/toolkit/modules/tests/browser/browser_web_channel.js b/toolkit/modules/tests/browser/browser_web_channel.js
index 9dfa59485b08..289e4d1d1441 100644
--- a/toolkit/modules/tests/browser/browser_web_channel.js
+++ b/toolkit/modules/tests/browser/browser_web_channel.js
@@ -23,10 +23,10 @@ var gTests = [
   {
     desc: "WebChannel generic message",
     run() {
-      return new Promise(function (resolve, reject) {
+      return new Promise(function (resolve) {
         let tab;
         let channel = new WebChannel("generic", Services.io.newURI(HTTP_PATH));
-        channel.listen(function (id, message, target) {
+        channel.listen(function (id, message) {
           is(id, "generic");
           is(message.something.nested, "hello");
           channel.stopListening();
@@ -44,9 +44,9 @@ var gTests = [
   {
     desc: "WebChannel generic message in a private window.",
     async run() {
-      let promiseTestDone = new Promise(function (resolve, reject) {
+      let promiseTestDone = new Promise(function (resolve) {
         let channel = new WebChannel("generic", Services.io.newURI(HTTP_PATH));
-        channel.listen(function (id, message, target) {
+        channel.listen(function (id, message) {
           is(id, "generic");
           is(message.something.nested, "hello");
           channel.stopListening();
@@ -66,7 +66,7 @@ var gTests = [
   {
     desc: "WebChannel two way communication",
     run() {
-      return new Promise(function (resolve, reject) {
+      return new Promise(function (resolve) {
         let tab;
         let channel = new WebChannel("twoway", Services.io.newURI(HTTP_PATH));
 
@@ -102,7 +102,7 @@ var gTests = [
         Services.io.newURI(HTTP_IFRAME_PATH)
       );
       let promiseTestDone = new Promise(function (resolve, reject) {
-        parentChannel.listen(function (id, message, sender) {
+        parentChannel.listen(function () {
           reject(new Error("WebChannel message incorrectly sent to parent"));
         });
 
@@ -218,14 +218,14 @@ var gTests = [
   {
     desc: "WebChannel multichannel",
     run() {
-      return new Promise(function (resolve, reject) {
+      return new Promise(function (resolve) {
         let tab;
         let channel = new WebChannel(
           "multichannel",
           Services.io.newURI(HTTP_PATH)
         );
 
-        channel.listen(function (id, message, sender) {
+        channel.listen(function (id) {
           is(id, "multichannel");
           gBrowser.removeTab(tab);
           resolve();
@@ -246,8 +246,8 @@ var gTests = [
       // an unsolicted message is sent from Chrome->Content which is then
       // echoed back. If the echo is received here, then the content
       // received the message.
-      let messagePromise = new Promise(function (resolve, reject) {
-        channel.listen(function (id, message, sender) {
+      let messagePromise = new Promise(function (resolve) {
+        channel.listen(function (id, message) {
           is(id, "echo");
           is(message.command, "unsolicited");
 
@@ -283,8 +283,8 @@ var gTests = [
       // an unsolicted message is sent from Chrome->Content which is then
       // echoed back. If the echo is received here, then the content
       // received the message.
-      let messagePromise = new Promise(function (resolve, reject) {
-        channel.listen(function (id, message, sender) {
+      let messagePromise = new Promise(function (resolve) {
+        channel.listen(function (id, message) {
           is(id, "echo");
           is(message.command, "unsolicited");
 
@@ -326,7 +326,7 @@ var gTests = [
       // and should not be echoed back. The second, `done`, is sent to the
       // correct principal and should be echoed back.
       let messagePromise = new Promise(function (resolve, reject) {
-        channel.listen(function (id, message, sender) {
+        channel.listen(function (id, message) {
           is(id, "echo");
 
           if (message.command === "done") {
@@ -435,8 +435,8 @@ var gTests = [
        * message.
        */
       let channel = new WebChannel("objects", Services.io.newURI(HTTP_PATH));
-      let testDonePromise = new Promise((resolve, reject) => {
-        channel.listen((id, message, sender) => {
+      let testDonePromise = new Promise(resolve => {
+        channel.listen((id, message) => {
           is(id, "objects");
           is(message.type, "string");
           resolve();
@@ -466,7 +466,7 @@ var gTests = [
       let testDonePromise = new Promise((resolve, reject) => {
         let sawObject = false;
         let sawString = false;
-        channel.listen((id, message, sender) => {
+        channel.listen((id, message) => {
           is(id, "objects");
           if (message.type === "object") {
             ok(!sawObject);
@@ -509,9 +509,9 @@ var gTests = [
       // The channel where we see the response when the content sees the error
       let echoChannel = new WebChannel("echo", Services.io.newURI(HTTP_PATH));
 
-      let testDonePromise = new Promise((resolve, reject) => {
+      let testDonePromise = new Promise(resolve => {
         // listen for the confirmation that content saw the error.
-        echoChannel.listen((id, message, sender) => {
+        echoChannel.listen((id, message) => {
           is(id, "echo");
           is(message.error, "oh no");
           is(message.errno, ERRNO_UNKNOWN_ERROR);
@@ -519,7 +519,7 @@ var gTests = [
         });
 
         // listen for a message telling us to simulate an error.
-        channel.listen((id, message, sender) => {
+        channel.listen((id, message) => {
           is(id, "error");
           is(message.command, "oops");
           throw new Error("oh no");
@@ -545,9 +545,9 @@ var gTests = [
       // The channel where we see the response when the content sees the error
       let echoChannel = new WebChannel("echo", Services.io.newURI(HTTP_PATH));
 
-      let testDonePromise = new Promise((resolve, reject) => {
+      let testDonePromise = new Promise(resolve => {
         // listen for the confirmation that content saw the error.
-        echoChannel.listen((id, message, sender) => {
+        echoChannel.listen((id, message) => {
           is(id, "echo");
           is(message.error, "No Such Channel");
           is(message.errno, ERRNO_NO_SUCH_CHANNEL);
diff --git a/toolkit/modules/tests/browser/head.js b/toolkit/modules/tests/browser/head.js
index 7c3f75b106fd..84bfad932801 100644
--- a/toolkit/modules/tests/browser/head.js
+++ b/toolkit/modules/tests/browser/head.js
@@ -87,7 +87,7 @@ function promiseTestHighlighterOutput(
     browser,
     [{ word, expectedResult, extraTest: extraTest.toSource() }],
     async function ({ word, expectedResult, extraTest }) {
-      return new Promise((resolve, reject) => {
+      return new Promise(resolve => {
         let stubbed = {};
         let callCounts = {
           insertCalls: [],
diff --git a/toolkit/modules/tests/modules/MockDocument.sys.mjs b/toolkit/modules/tests/modules/MockDocument.sys.mjs
index 163beb84503f..d4c2b0720539 100644
--- a/toolkit/modules/tests/modules/MockDocument.sys.mjs
+++ b/toolkit/modules/tests/modules/MockDocument.sys.mjs
@@ -40,7 +40,7 @@ export const MockDocument = {
     // Mock the document.location object so we can unit test without a frame. We use a proxy
     // instead of just assigning to the property since it's not configurable or writable.
     let document = new Proxy(aDoc, {
-      get(target, property, receiver) {
+      get(target, property) {
         // document.location is normally null when a document is outside of a "browsing context".
         // See https://html.spec.whatwg.org/#the-location-interface
         if (property == "location") {
diff --git a/toolkit/modules/tests/xpcshell/test_DeferredTask.js b/toolkit/modules/tests/xpcshell/test_DeferredTask.js
index e6c58e03db1d..cb1cc2d6001e 100644
--- a/toolkit/modules/tests/xpcshell/test_DeferredTask.js
+++ b/toolkit/modules/tests/xpcshell/test_DeferredTask.js
@@ -389,7 +389,7 @@ add_test(function test_finalize() {
   let finalized = false;
 
   // Let idleDispatch take longer.
-  replaceIdleDispatch((callback, timeout) => {
+  replaceIdleDispatch(callback => {
     Assert.ok(!idleStarted);
     idleStarted = true;
     do_timeout(T, callback);
diff --git a/toolkit/modules/tests/xpcshell/test_FinderIterator.js b/toolkit/modules/tests/xpcshell/test_FinderIterator.js
index fcbe97ba5f73..5125740c55ca 100644
--- a/toolkit/modules/tests/xpcshell/test_FinderIterator.js
+++ b/toolkit/modules/tests/xpcshell/test_FinderIterator.js
@@ -7,7 +7,7 @@ let finderIterator = new FinderIterator();
 var gFindResults = [];
 // Stub the method that instantiates nsIFind and does all the interaction with
 // the docShell to be searched through.
-finderIterator._iterateDocument = function* (word, window, finder) {
+finderIterator._iterateDocument = function* () {
   for (let range of gFindResults) {
     yield range;
   }
@@ -117,7 +117,7 @@ add_task(async function test_valid_arguments() {
     entireWord: false,
     finder: gMockFinder,
     listener: {
-      onIteratorRangeFound(range) {
+      onIteratorRangeFound() {
         ++count;
       },
     },
@@ -136,7 +136,7 @@ add_task(async function test_valid_arguments() {
       finderIterator.start({
         entireWord: false,
         listener: {
-          onIteratorRangeFound(range) {
+          onIteratorRangeFound() {
             ++count;
           },
         },
@@ -154,7 +154,7 @@ add_task(async function test_valid_arguments() {
         caseSensitive: false,
         entireWord: false,
         listener: {
-          onIteratorRangeFound(range) {
+          onIteratorRangeFound() {
             ++count;
           },
         },
@@ -170,7 +170,7 @@ add_task(async function test_valid_arguments() {
       finderIterator.start({
         caseSensitive: false,
         listener: {
-          onIteratorRangeFound(range) {
+          onIteratorRangeFound() {
             ++count;
           },
         },
@@ -188,7 +188,7 @@ add_task(async function test_valid_arguments() {
         caseSensitive: false,
         entireWord: false,
         listener: {
-          onIteratorRangeFound(range) {
+          onIteratorRangeFound() {
             ++count;
           },
         },
@@ -221,7 +221,7 @@ add_task(async function test_valid_arguments() {
         entireWord: true,
         finder: gMockFinder,
         listener: {
-          onIteratorRangeFound(range) {
+          onIteratorRangeFound() {
             ++count;
           },
         },
@@ -246,7 +246,7 @@ add_task(async function test_stop() {
     entireWord: false,
     finder: gMockFinder,
     listener: {
-      onIteratorRangeFound(range) {
+      onIteratorRangeFound() {
         ++count;
       },
     },
@@ -274,7 +274,7 @@ add_task(async function test_reset() {
     entireWord: false,
     finder: gMockFinder,
     listener: {
-      onIteratorRangeFound(range) {
+      onIteratorRangeFound() {
         ++count;
       },
     },
@@ -317,7 +317,7 @@ add_task(async function test_parallel_starts() {
     entireWord: false,
     finder: gMockFinder,
     listener: {
-      onIteratorRangeFound(range) {
+      onIteratorRangeFound() {
         ++count;
       },
     },
@@ -334,7 +334,7 @@ add_task(async function test_parallel_starts() {
     entireWord: false,
     finder: gMockFinder,
     listener: {
-      onIteratorRangeFound(range) {
+      onIteratorRangeFound() {
         ++count2;
       },
     },
@@ -385,7 +385,7 @@ add_task(async function test_allowDistance() {
     entireWord: false,
     finder: gMockFinder,
     listener: {
-      onIteratorRangeFound(range) {
+      onIteratorRangeFound() {
         ++count;
       },
     },
@@ -399,7 +399,7 @@ add_task(async function test_allowDistance() {
     entireWord: false,
     finder: gMockFinder,
     listener: {
-      onIteratorRangeFound(range) {
+      onIteratorRangeFound() {
         ++count2;
       },
     },
@@ -414,7 +414,7 @@ add_task(async function test_allowDistance() {
     entireWord: false,
     finder: gMockFinder,
     listener: {
-      onIteratorRangeFound(range) {
+      onIteratorRangeFound() {
         ++count3;
       },
     },
diff --git a/toolkit/modules/tests/xpcshell/test_GMPInstallManager.js b/toolkit/modules/tests/xpcshell/test_GMPInstallManager.js
index a0d12b8a6adb..5198ca9eb59b 100644
--- a/toolkit/modules/tests/xpcshell/test_GMPInstallManager.js
+++ b/toolkit/modules/tests/xpcshell/test_GMPInstallManager.js
@@ -1175,7 +1175,7 @@ add_test(function test_installAddon_noServer() {
       GMPInstallManager.overrideLeaveDownloadedZip = true;
       let installPromise = installManager.installAddon(gmpAddon);
       installPromise.then(
-        extractedPaths => {
+        () => {
           do_throw("No server for install should reject");
         },
         err => {
@@ -1324,8 +1324,8 @@ function mockRequest(inputStatus, inputResponse, options) {
   this._options = options || {};
 }
 mockRequest.prototype = {
-  overrideMimeType(aMimetype) {},
-  setRequestHeader(aHeader, aValue) {},
+  overrideMimeType() {},
+  setRequestHeader() {},
   status: null,
   channel: { set notificationCallbacks(aVal) {} },
   open(aMethod, aUrl) {
@@ -1339,7 +1339,7 @@ mockRequest.prototype = {
   },
   responseXML: null,
   responseText: null,
-  send(aBody) {
+  send() {
     executeSoon(() => {
       try {
         if (this._options.dropRequest) {
@@ -1427,9 +1427,8 @@ mockRequest.prototype = {
       }
     }
   },
-  addEventListener(aEvent, aValue, aCapturing) {
-    // eslint-disable-next-line no-eval
-    eval("this._on" + aEvent + " = aValue");
+  addEventListener(aEvent, aValue) {
+    this[`_on${aEvent}`] = aValue;
   },
   get wrappedJSObject() {
     return this;
diff --git a/toolkit/modules/tests/xpcshell/test_Integration.js b/toolkit/modules/tests/xpcshell/test_Integration.js
index 8213e32592f4..d0f53cc22a1b 100644
--- a/toolkit/modules/tests/xpcshell/test_Integration.js
+++ b/toolkit/modules/tests/xpcshell/test_Integration.js
@@ -170,7 +170,7 @@ add_task(async function test_override_super_multiple() {
  * ensures that this does not block other functions from being registered.
  */
 add_task(async function test_override_error() {
-  let errorOverrideFn = base => {
+  let errorOverrideFn = () => {
     throw new Error("Expected error.");
   };
 
diff --git a/toolkit/modules/tests/xpcshell/test_sqlite.js b/toolkit/modules/tests/xpcshell/test_sqlite.js
index e0a79e137df7..bea349ded4f6 100644
--- a/toolkit/modules/tests/xpcshell/test_sqlite.js
+++ b/toolkit/modules/tests/xpcshell/test_sqlite.js
@@ -334,12 +334,9 @@ add_task(async function test_execute_invalid_statement() {
   await new Promise(resolve => {
     Assert.equal(c._connectionData._anonymousStatements.size, 0);
 
-    c.execute("SELECT invalid FROM unknown").then(
-      do_throw,
-      function onError(error) {
-        resolve();
-      }
-    );
+    c.execute("SELECT invalid FROM unknown").then(do_throw, function onError() {
+      resolve();
+    });
   });
 
   // Ensure we don't leak the statement instance.
@@ -366,15 +363,11 @@ add_task(async function test_on_row_exception_ignored() {
   }
 
   let i = 0;
-  let hasResult = await c.execute(
-    "SELECT * FROM DIRS",
-    null,
-    function onRow(row) {
-      i++;
+  let hasResult = await c.execute("SELECT * FROM DIRS", null, function onRow() {
+    i++;
 
-      throw new Error("Some silly error.");
-    }
-  );
+    throw new Error("Some silly error.");
+  });
 
   Assert.equal(hasResult, true);
   Assert.equal(i, 10);
@@ -418,7 +411,7 @@ add_task(async function test_on_row_stop_iteration() {
   let hasResult = await c.execute(
     `SELECT * FROM dirs WHERE path="nonexistent"`,
     null,
-    function onRow(row) {
+    function onRow() {
       i++;
     }
   );
@@ -473,7 +466,7 @@ add_task(async function test_execute_transaction_rollback() {
 
     // We should never get here.
     do_throw();
-  }).then(do_throw, function onError(error) {
+  }).then(do_throw, function onError() {
     deferred.resolve();
   });
 
@@ -490,7 +483,7 @@ add_task(async function test_close_during_transaction() {
 
   await c.execute("INSERT INTO dirs (path) VALUES ('foo')");
 
-  let promise = c.executeTransaction(async function transaction(conn) {
+  let promise = c.executeTransaction(async function transaction() {
     await c.execute("INSERT INTO dirs (path) VALUES ('bar')");
   });
   await c.close();
@@ -801,7 +794,7 @@ add_task(async function test_discard_while_active() {
   let discarded = -1;
   let first = true;
   let sql = "SELECT * FROM dirs";
-  await c.executeCached(sql, null, function onRow(row) {
+  await c.executeCached(sql, null, function onRow() {
     if (!first) {
       return;
     }
@@ -1010,7 +1003,7 @@ add_task(async function test_direct() {
 
   let deferred = Promise.withResolvers();
   begin.executeAsync({
-    handleCompletion(reason) {
+    handleCompletion() {
       deferred.resolve();
     },
   });
@@ -1021,7 +1014,7 @@ add_task(async function test_direct() {
   deferred = Promise.withResolvers();
   print("Executing async.");
   statement.executeAsync({
-    handleResult(resultSet) {},
+    handleResult() {},
 
     handleError(error) {
       print(
@@ -1031,7 +1024,7 @@ add_task(async function test_direct() {
       deferred.reject();
     },
 
-    handleCompletion(reason) {
+    handleCompletion() {
       print("Completed.");
       deferred.resolve();
     },
@@ -1041,7 +1034,7 @@ add_task(async function test_direct() {
 
   deferred = Promise.withResolvers();
   end.executeAsync({
-    handleCompletion(reason) {
+    handleCompletion() {
       deferred.resolve();
     },
   });
diff --git a/toolkit/modules/tests/xpcshell/test_web_channel.js b/toolkit/modules/tests/xpcshell/test_web_channel.js
index 6d62762e979a..a45f52efdeaa 100644
--- a/toolkit/modules/tests/xpcshell/test_web_channel.js
+++ b/toolkit/modules/tests/xpcshell/test_web_channel.js
@@ -37,7 +37,7 @@ var MockWebChannelBroker = {
  * Test channel listening with originOrPermission being an nsIURI.
  */
 add_task(function test_web_channel_listen() {
-  return new Promise((resolve, reject) => {
+  return new Promise(resolve => {
     let channel = new WebChannel(
       VALID_WEB_CHANNEL_ID,
       VALID_WEB_CHANNEL_ORIGIN,
@@ -94,7 +94,7 @@ add_task(function test_web_channel_listen() {
  * Test channel listening with originOrPermission being a permission string.
  */
 add_task(function test_web_channel_listen_permission() {
-  return new Promise((resolve, reject) => {
+  return new Promise(resolve => {
     // add a new permission
     PermissionTestUtils.add(
       VALID_WEB_CHANNEL_ORIGIN,
diff --git a/toolkit/modules/tests/xpcshell/test_web_channel_broker.js b/toolkit/modules/tests/xpcshell/test_web_channel_broker.js
index 232e02e93541..3e3d4efc0e99 100644
--- a/toolkit/modules/tests/xpcshell/test_web_channel_broker.js
+++ b/toolkit/modules/tests/xpcshell/test_web_channel_broker.js
@@ -44,7 +44,7 @@ add_test(function test_web_channel_broker_channel_map() {
  * Test WebChannelBroker _listener test
  */
 add_task(function test_web_channel_broker_listener() {
-  return new Promise((resolve, reject) => {
+  return new Promise(resolve => {
     var channel = {
       id: VALID_WEB_CHANNEL_ID,
       _originCheckCallback: requestPrincipal => {
diff --git a/toolkit/xre/test/browser_checkdllblockliststate.js b/toolkit/xre/test/browser_checkdllblockliststate.js
index 759c9b36353e..cddd08699198 100644
--- a/toolkit/xre/test/browser_checkdllblockliststate.js
+++ b/toolkit/xre/test/browser_checkdllblockliststate.js
@@ -5,7 +5,7 @@
 add_task(async function test() {
   await BrowserTestUtils.withNewTab(
     { gBrowser, url: "about:blank" },
-    function (browser) {
+    function () {
       ok(
         Services.appinfo.windowsDLLBlocklistStatus,
         "Windows dll blocklist status should be true, indicating it is " +
diff --git a/toolkit/xre/test/test_launch_without_hang.js b/toolkit/xre/test/test_launch_without_hang.js
index feacae36d41d..eef1ece226b5 100644
--- a/toolkit/xre/test/test_launch_without_hang.js
+++ b/toolkit/xre/test/test_launch_without_hang.js
@@ -100,7 +100,7 @@ function terminateFirefox(completion) {
   process.init(file);
 
   let processObserver = {
-    observe: function PO_observe(aSubject, aTopic, aData) {
+    observe: function PO_observe(aSubject, aTopic) {
       info("topic: " + aTopic + ", process exitValue: " + process.exitValue);
 
       Assert.equal(
@@ -135,7 +135,7 @@ function launchProcess(file, args, env, timeoutMS, handler, attemptCount) {
   state.attempt = attemptCount;
 
   state.processObserver = {
-    observe: function PO_observe(aSubject, aTopic, aData) {
+    observe: function PO_observe(aSubject, aTopic) {
       if (!state.appTimer) {
         // the app timer has been canceled; this process has timed out already so don't process further.
         handler(false);
@@ -170,7 +170,7 @@ function launchProcess(file, args, env, timeoutMS, handler, attemptCount) {
 
   // The timer callback to kill the process if it takes too long.
   state.appTimerCallback = {
-    notify: function TC_notify(aTimer) {
+    notify: function TC_notify() {
       state.appTimer = null;
 
       info("Restoring environment variables");
diff --git a/toolkit/xre/test/win/mochitest/browser_env_path_long.js b/toolkit/xre/test/win/mochitest/browser_env_path_long.js
index 9bc63214b02e..33832bba77a8 100644
--- a/toolkit/xre/test/win/mochitest/browser_env_path_long.js
+++ b/toolkit/xre/test/win/mochitest/browser_env_path_long.js
@@ -6,7 +6,7 @@
 add_task(async function test() {
   await BrowserTestUtils.withNewTab(
     { gBrowser, url: "about:blank" },
-    function (browser) {
+    function () {
       ok(
         true,
         "Browser should start even with potentially pathologically long PATH."