Bug 232598 - Return null for unset attributes in XUL. r=smaug,devtools-reviewers,omc-reviewers,zombie,nchevobbe,settings-reviewers,application-update-reviewers,credential-management-reviewers,mossop,aminomancer,bytesized,issammani,sessionstore-reviewers,dao

I just got bit by this in bug 1873833, let's just fix it. There isn't
all that much stuff depending on it anymore.

Differential Revision: https://phabricator.services.mozilla.com/D204496

browser/base/content/browser.js

@@ -8658,7 +8658,7 @@ function switchToTabHavingURI(
         ignoreQueryString || replaceQueryString,
         ignoreFragmentWhenComparing
       );
-      let browserUserContextId = browser.getAttribute("usercontextid");
+      let browserUserContextId = browser.getAttribute("usercontextid") || "";
       if (aUserContextId != null && aUserContextId != browserUserContextId) {
         continue;
       }

browser/base/content/test/favicons/browser_missing_favicon.js

@@ -28,7 +28,7 @@ add_task(async () => {
       is(browser.mIconURL, null, "Should have blanked the icon.");
       is(
         gBrowser.getTabForBrowser(browser).getAttribute("image"),
-        "",
+        null,
         "Should have blanked the tab icon."
       );
     }

browser/base/content/test/siteIdentity/head.js

@@ -244,12 +244,12 @@ async function assertMixedContentBlockingState(tabbrowser, states = {}) {
   );
   gIdentityHandler._identityIconBox.click();
   await promisePanelOpen;
-  let popupAttr = doc
+  let popupAttr =
-    .getElementById("identity-popup")
+    doc.getElementById("identity-popup").getAttribute("mixedcontent") || "";
-    .getAttribute("mixedcontent");
+  let bodyAttr =
-  let bodyAttr = doc
+    doc
-    .getElementById("identity-popup-securityView-extended-info")
+      .getElementById("identity-popup-securityView-extended-info")
-    .getAttribute("mixedcontent");
+      .getAttribute("mixedcontent") || "";
 
   is(
     popupAttr.includes("active-loaded"),

browser/base/content/test/sync/browser_sync.js

@@ -772,7 +772,7 @@ function checkSyncNowButtons(syncing, tooltip = null) {
   for (const syncButton of syncButtons) {
     is(
       syncButton.getAttribute("syncstatus"),
-      syncing ? "active" : "",
+      syncing ? "active" : null,
       "button active has the right value"
     );
     if (tooltip) {

browser/base/content/test/tabPrompts/browser_auth_spoofing_protection.js

@@ -119,7 +119,7 @@ async function waitForDialog(doConfirmPrompt, crossDomain, prefEnabled) {
     } else {
       Assert.equal(
         dialog._overlay.getAttribute("hideContent"),
-        "",
+        null,
         "Dialog overlay does not hide the current sites content"
       );
       Assert.equal(
@@ -137,7 +137,7 @@ async function waitForDialog(doConfirmPrompt, crossDomain, prefEnabled) {
   } else {
     Assert.equal(
       dialog._overlay.getAttribute("hideContent"),
-      "",
+      null,
       "Dialog overlay does not hide the current sites content"
     );
     Assert.equal(

browser/base/content/test/tabs/browser_lazy_tab_browser_events.js

@@ -93,10 +93,10 @@ add_task(async function test_hidden_muted_lazy_tabs_and_swapping() {
   mutedTab.toggleMuteAudio();
   gBrowser.hideTab(hiddenTab);
 
-  is(lazyTab.linkedPanel, "", "lazyTab is lazy");
+  is(lazyTab.linkedPanel, null, "lazyTab is lazy");
-  is(hiddenTab.linkedPanel, "", "hiddenTab is lazy");
+  is(hiddenTab.linkedPanel, null, "hiddenTab is lazy");
-  is(mutedTab.linkedPanel, "", "mutedTab is lazy");
+  is(mutedTab.linkedPanel, null, "mutedTab is lazy");
-  is(normalTab.linkedPanel, "", "normalTab is lazy");
+  is(normalTab.linkedPanel, null, "normalTab is lazy");
 
   ok(mutedTab.linkedBrowser.audioMuted, "mutedTab is muted");
   ok(hiddenTab.hidden, "hiddenTab is hidden");
@@ -117,7 +117,7 @@ add_task(async function test_hidden_muted_lazy_tabs_and_swapping() {
   });
   gBrowser.swapBrowsersAndCloseOther(lazyTab, mutedTab);
   tabEventTracker.checkExpectations();
-  is(lazyTab.linkedPanel, "", "muted lazyTab is still lazy");
+  is(lazyTab.linkedPanel, null, "muted lazyTab is still lazy");
   ok(lazyTab.linkedBrowser.audioMuted, "muted lazyTab is now muted");
   ok(!lazyTab.hidden, "muted lazyTab is not hidden");
 
@@ -133,7 +133,7 @@ add_task(async function test_hidden_muted_lazy_tabs_and_swapping() {
   });
   gBrowser.swapBrowsersAndCloseOther(lazyTab, hiddenTab);
   tabEventTracker.checkExpectations();
-  is(lazyTab.linkedPanel, "", "hidden lazyTab is still lazy");
+  is(lazyTab.linkedPanel, null, "hidden lazyTab is still lazy");
   ok(!lazyTab.linkedBrowser.audioMuted, "hidden lazyTab is not muted any more");
   ok(lazyTab.hidden, "hidden lazyTab has been hidden");
 
@@ -149,7 +149,7 @@ add_task(async function test_hidden_muted_lazy_tabs_and_swapping() {
   });
   gBrowser.swapBrowsersAndCloseOther(lazyTab, normalTab);
   tabEventTracker.checkExpectations();
-  is(lazyTab.linkedPanel, "", "normal lazyTab is still lazy");
+  is(lazyTab.linkedPanel, null, "normal lazyTab is still lazy");
   ok(!lazyTab.linkedBrowser.audioMuted, "normal lazyTab is not muted any more");
   ok(!lazyTab.hidden, "normal lazyTab is not hidden any more");
 

browser/base/content/test/tabs/browser_multiselect_tabs_move_to_new_window_contextmenu.js

@@ -61,9 +61,9 @@ add_task(async function testLazyTabs() {
     await triggerClickOn(oldTabs[i], { ctrlKey: true });
   }
 
-  isnot(oldTabs[0].linkedPanel, "", `Old tab 0 shouldn't be lazy`);
+  isnot(oldTabs[0].linkedPanel, null, `Old tab 0 shouldn't be lazy`);
   for (let i = 1; i < numTabs; ++i) {
-    is(oldTabs[i].linkedPanel, "", `Old tab ${i} should be lazy`);
+    is(oldTabs[i].linkedPanel, null, `Old tab ${i} should be lazy`);
   }
 
   is(gBrowser.multiSelectedTabsCount, numTabs, `${numTabs} multiselected tabs`);
@@ -79,11 +79,11 @@ add_task(async function testLazyTabs() {
       if (i == 0) {
         isnot(
           oldTab.linkedPanel,
-          "",
+          null,
           `Old tab ${i} should continue not being lazy`
         );
       } else if (i > 0) {
-        is(oldTab.linkedPanel, "", `Old tab ${i} should continue being lazy`);
+        is(oldTab.linkedPanel, null, `Old tab ${i} should continue being lazy`);
       } else {
         return;
       }
@@ -101,9 +101,13 @@ add_task(async function testLazyTabs() {
   await tabsMoved;
   let newTabs = newWindow.gBrowser.tabs;
 
-  isnot(newTabs[0].linkedPanel, "", `New tab 0 should continue not being lazy`);
+  isnot(
+    newTabs[0].linkedPanel,
+    null,
+    `New tab 0 should continue not being lazy`
+  );
   for (let i = 1; i < numTabs; ++i) {
-    is(newTabs[i].linkedPanel, "", `New tab ${i} should continue being lazy`);
+    is(newTabs[i].linkedPanel, null, `New tab ${i} should continue being lazy`);
   }
 
   is(

browser/base/content/test/tabs/browser_pinnedTabs_closeByKeyboard.js

@@ -12,7 +12,7 @@ function test() {
 
     is(
       elemAttr("key_close", "disabled"),
-      "",
+      null,
       "key_closed should always be enabled"
     );
     is(

browser/base/content/test/tabs/browser_tab_tooltips.js

@@ -57,7 +57,7 @@ add_task(async function () {
   );
   is(
     tooltip.getAttribute("position"),
-    "",
+    null,
     "tooltip position attribute for tab"
   );
 

browser/base/content/test/webextensions/browser_extension_update_background.js

@@ -87,7 +87,7 @@ async function backgroundUpdateTest(url, id, checkIconFn) {
   let addonId = addon.id;
 
   ok(addon, "Addon was installed");
-  is(getBadgeStatus(), "", "Should not start out with an addon alert badge");
+  is(getBadgeStatus(), null, "Should not start out with an addon alert badge");
 
   // Trigger an update check and wait for the update for this addon
   // to be downloaded.
@@ -156,7 +156,7 @@ async function backgroundUpdateTest(url, id, checkIconFn) {
   BrowserTestUtils.removeTab(tab);
 
   // Alert badge and hamburger menu items should be gone
-  is(getBadgeStatus(), "", "Addon alert badge should be gone");
+  is(getBadgeStatus(), null, "Addon alert badge should be gone");
 
   await gCUITestUtils.openMainMenu();
   addons = PanelUI.addonNotificationContainer;
@@ -205,7 +205,7 @@ async function backgroundUpdateTest(url, id, checkIconFn) {
 
   BrowserTestUtils.removeTab(tab);
 
-  is(getBadgeStatus(), "", "Addon alert badge should be gone");
+  is(getBadgeStatus(), null, "Addon alert badge should be gone");
 
   await addon.uninstall();
   await SpecialPowers.popPrefEnv();

browser/base/content/test/webextensions/browser_extension_update_background_noprompt.js

@@ -81,7 +81,7 @@ async function testNoPrompt(origUrl, id) {
   await updatePromise;
 
   // There should be no notifications about the update
-  is(getBadgeStatus(), "", "Should not have addon alert badge");
+  is(getBadgeStatus(), null, "Should not have addon alert badge");
 
   await gCUITestUtils.openMainMenu();
   let addons = PanelUI.addonNotificationContainer;

browser/base/content/test/webrtc/browser_devices_get_user_media_anim.js

@@ -58,7 +58,7 @@ var gTests = [
         );
         is(
           gBrowser.selectedTab.getAttribute("sharing"),
-          "",
+          null,
           "the new tab doesn't have the 'sharing' attribute"
         );
         is(
@@ -89,7 +89,7 @@ var gTests = [
         await TestUtils.waitForCondition(() => !tab.getAttribute("sharing"));
         is(
           tab.getAttribute("sharing"),
-          "",
+          null,
           "the tab no longer has the 'sharing' attribute after closing the stream"
         );
       }

browser/base/content/utilityOverlay.js

@@ -294,7 +294,7 @@ function closeMenus(node) {
  *        to check if the close command key was pressed in aEvent.
  */
 function eventMatchesKey(aEvent, aKey) {
-  let keyPressed = aKey.getAttribute("key").toLowerCase();
+  let keyPressed = (aKey.getAttribute("key") || "").toLowerCase();
   let keyModifiers = aKey.getAttribute("modifiers");
   let modifiers = ["Alt", "Control", "Meta", "Shift"];
 
@@ -341,7 +341,7 @@ function gatherTextUnder(root) {
     } else if (HTMLImageElement.isInstance(node)) {
       // If it has an "alt" attribute, add that.
       var altText = node.getAttribute("alt");
-      if (altText && altText != "") {
+      if (altText) {
         text += " " + altText;
       }
     }

browser/components/aboutlogins/tests/browser/browser_sessionRestore.js

@@ -35,7 +35,7 @@ add_task(async function () {
     createLazyBrowser: true,
   });
 
-  Assert.equal(lazyTab.linkedPanel, "", "Tab is lazy");
+  Assert.equal(lazyTab.linkedPanel, null, "Tab is lazy");
   let tabLoaded = new Promise(resolve => {
     gBrowser.addTabsProgressListener({
       async onLocationChange(aBrowser) {

browser/components/contextualidentity/test/browser/browser_guessusercontext.js

@@ -93,7 +93,7 @@ add_task(async function test() {
   openURIFromExternal(HOST_EXAMPLE.spec + "?new");
   is(
     gBrowser.selectedTab.getAttribute("usercontextid"),
-    "",
+    null,
     "opener flow with default user context ID forced by pref"
   );
 });

browser/components/customizableui/test/browser_customization_context_menus.js

@@ -549,7 +549,7 @@ add_task(async function custom_context_menus() {
   await startCustomizing();
   is(
     widget.getAttribute("context"),
-    "",
+    null,
     "Should not have own context menu in the toolbar now that we're customizing."
   );
   is(
@@ -562,7 +562,7 @@ add_task(async function custom_context_menus() {
   simulateItemDrag(widget, panel);
   is(
     widget.getAttribute("context"),
-    "",
+    null,
     "Should not have own context menu when in the panel."
   );
   is(
@@ -577,7 +577,7 @@ add_task(async function custom_context_menus() {
   );
   is(
     widget.getAttribute("context"),
-    "",
+    null,
     "Should not have own context menu when back in toolbar because we're still customizing."
   );
   is(

browser/components/customizableui/test/browser_open_in_lazy_tab.js

@@ -9,7 +9,7 @@ add_task(async function open_customize_mode_in_lazy_tab() {
   });
   gCustomizeMode.setTab(tab);
 
-  is(tab.linkedPanel, "", "Tab should be lazy");
+  is(tab.linkedPanel, null, "Tab should be lazy");
 
   let title = gNavigatorBundle.getFormattedString("customizeMode.tabTitle", [
     document.getElementById("bundle_brand").getString("brandShortName"),

browser/components/customizableui/test/browser_synced_tabs_menu.js

@@ -378,7 +378,7 @@ add_task(async function () {
   // There is a single node saying there's no tabs for the client.
   node = node.nextElementSibling;
   is(node.nodeName, "label", "node is a label");
-  is(node.getAttribute("itemtype"), "", "node is neither a tab nor a client");
+  is(node.getAttribute("itemtype"), null, "node is neither a tab nor a client");
 
   node = node.nextElementSibling;
   is(node, null, "no more siblings");

browser/components/extensions/test/browser/browser_ext_browserAction_context.js

@@ -184,7 +184,11 @@ async function runTests(options) {
     is(getListStyleImage(button), details.icon, "icon URL is correct");
     is(button.getAttribute("tooltiptext"), title, "image title is correct");
     is(button.getAttribute("label"), title, "image label is correct");
-    is(button.getAttribute("badge"), details.badge, "badge text is correct");
+    is(
+      button.getAttribute("badge") || "",
+      details.badge,
+      "badge text is correct"
+    );
     is(
       button.getAttribute("disabled") == "true",
       !details.enabled,

browser/components/extensions/test/browser/browser_ext_contextMenus_icons.js

@@ -269,7 +269,7 @@ add_task(async function test_manifest_without_icons() {
   let items = menu.getElementsByAttribute("label", "first item");
   is(items.length, 1, "Found first item");
   // manifest.json does not declare icons, so the root menu item shouldn't have an icon either.
-  is(items[0].getAttribute("image"), "", "Root menu must not have an icon");
+  is(items[0].getAttribute("image"), null, "Root menu must not have an icon");
 
   await closeExtensionContextMenu(items[0]);
   await extension.awaitMessage("added-second-item");
@@ -281,7 +281,7 @@ add_task(async function test_manifest_without_icons() {
   is(items.length, 1, "Auto-generated root item exists");
   is(
     items[0].getAttribute("image"),
-    "",
+    null,
     "Auto-generated menu root must not have an icon"
   );
 
@@ -464,7 +464,7 @@ add_task(async function test_child_icon_update() {
   contextMenuChild2 = contextMenu.getElementsByAttribute("label", "child2")[0];
   is(
     contextMenuChild2.getAttribute("image"),
-    "",
+    null,
     "Second child should not have an icon"
   );
 

browser/components/places/content/places.js

@@ -1168,7 +1168,7 @@ var ViewMenu = {
         menuitem.setAttribute("type", "radio");
         menuitem.setAttribute("name", "columns");
         // This column is the sort key. Its item is checked.
-        if (column.getAttribute("sortDirection") != "") {
+        if (column.hasAttribute("sortDirection")) {
           menuitem.setAttribute("checked", "true");
         }
       } else if (type == "checkbox") {

browser/components/places/tests/browser/browser_bookmark_context_menu_contents.js

@@ -131,14 +131,14 @@ let checkContextMenu = async (cbfunc, optionItems, doc = document) => {
     if (expectedOptionItems.includes("placesContext_open")) {
       Assert.equal(
         doc.getElementById("placesContext_open").getAttribute("default"),
-        loadBookmarksInNewTab ? "" : "true",
+        loadBookmarksInNewTab ? null : "true",
         `placesContext_open has the correct "default" attribute when loadBookmarksInTabs = ${loadBookmarksInNewTab}`
       );
     }
     if (expectedOptionItems.includes("placesContext_open:newtab")) {
       Assert.equal(
         doc.getElementById("placesContext_open:newtab").getAttribute("default"),
-        loadBookmarksInNewTab ? "true" : "",
+        loadBookmarksInNewTab ? "true" : null,
         `placesContext_open:newtab has the correct "default" attribute when loadBookmarksInTabs = ${loadBookmarksInNewTab}`
       );
     }

browser/components/pocket/test/browser_pocket_button_icon_state.js

@@ -72,7 +72,11 @@ function checkPanelClosed() {
   let pocketButton = document.getElementById("save-to-pocket-button");
   // Something should have closed the Pocket panel, icon should no longer be red.
   is(pocketButton.open, false, "Pocket button is closed");
-  is(pocketButton.getAttribute("pocketed"), "", "Pocket item is not pocketed");
+  is(
+    pocketButton.getAttribute("pocketed"),
+    null,
+    "Pocket item is not pocketed"
+  );
 }
 
 test_runner(async function test_pocketButtonState_changeTabs({ sandbox }) {

browser/components/preferences/tests/browser_applications_selection.js

@@ -335,10 +335,12 @@ add_task(async function sortingCheck() {
       "Number of items should not change."
     );
     for (let i = 0; i < siteItems.length - 1; ++i) {
-      let aType = siteItems[i].getAttribute("actionDescription").toLowerCase();
+      let aType = (
-      let bType = siteItems[i + 1]
+        siteItems[i].getAttribute("actionDescription") || ""
-        .getAttribute("actionDescription")
+      ).toLowerCase();
-        .toLowerCase();
+      let bType = (
+        siteItems[i + 1].getAttribute("actionDescription") || ""
+      ).toLowerCase();
       let result = 0;
       if (aType > bType) {
         result = 1;
@@ -375,10 +377,12 @@ add_task(async function sortingCheck() {
       "Number of items should not change."
     );
     for (let i = 0; i < siteItems.length - 1; ++i) {
-      let aType = siteItems[i].getAttribute("typeDescription").toLowerCase();
+      let aType = (
-      let bType = siteItems[i + 1]
+        siteItems[i].getAttribute("typeDescription") || ""
-        .getAttribute("typeDescription")
+      ).toLowerCase();
-        .toLowerCase();
+      let bType = (
+        siteItems[i + 1].getAttribute("typeDescription") || ""
+      ).toLowerCase();
       let result = 0;
       if (aType > bType) {
         result = 1;

browser/components/preferences/tests/browser_contentblocking.js

@@ -1021,7 +1021,7 @@ add_task(async function testDisableTPCheckBoxDisablesEmailTP() {
   // Verify the checkbox is unchecked after clicking.
   is(
     tpCheckbox.getAttribute("checked"),
-    "",
+    null,
     "Tracking protection checkbox is unchecked"
   );
 

browser/components/preferences/tests/browser_subdialogs.js

@@ -173,7 +173,7 @@ async function close_subdialog_and_test_generic_end_state(
       );
       Assert.equal(
         frame.getAttribute("style"),
-        "",
+        null,
         "inline styles should be cleared"
       );
       Assert.equal(

browser/components/sessionstore/SessionStore.sys.mjs

@@ -3635,7 +3635,7 @@ var SessionStoreInternal = {
     }
 
     // Create a new tab.
-    let userContextId = aTab.getAttribute("usercontextid");
+    let userContextId = aTab.getAttribute("usercontextid") || "";
 
     let tabOptions = {
       userContextId,

browser/components/sessionstore/test/browser_sessionStoreContainer.js

@@ -14,7 +14,7 @@ add_task(async function () {
     await promiseBrowserLoaded(browser);
 
     let tab2 = gBrowser.duplicateTab(tab);
-    Assert.equal(tab2.getAttribute("usercontextid"), i);
+    Assert.equal(tab2.getAttribute("usercontextid") || "", i);
     let browser2 = tab2.linkedBrowser;
     await promiseTabRestored(tab2);
 

browser/components/uitour/test/browser_UITour3.js

@@ -81,7 +81,7 @@ add_UITour_task(async function test_info_buttons_1() {
   );
   is(
     buttons.children[0].getAttribute("image"),
-    "",
+    null,
     "Text should have no image"
   );
   is(buttons.children[0].className, "", "Text should have no class");
@@ -94,7 +94,7 @@ add_UITour_task(async function test_info_buttons_1() {
   );
   is(
     buttons.children[1].getAttribute("image"),
-    "",
+    null,
     "Link should have no image"
   );
   is(buttons.children[1].className, "button-link", "Check link class");
@@ -107,7 +107,7 @@ add_UITour_task(async function test_info_buttons_1() {
   );
   is(
     buttons.children[2].getAttribute("image"),
-    "",
+    null,
     "First button should have no image"
   );
   is(buttons.children[2].className, "", "Button 1 should have no class");
@@ -173,7 +173,7 @@ add_UITour_task(async function test_info_buttons_2() {
   );
   is(
     buttons.children[1].getAttribute("image"),
-    "",
+    null,
     "Link should have no image"
   );
   ok(
@@ -188,7 +188,7 @@ add_UITour_task(async function test_info_buttons_2() {
   );
   is(
     buttons.children[2].getAttribute("image"),
-    "",
+    null,
     "First button should have no image"
   );
 

browser/components/urlbar/tests/browser/browser_UrlbarInput_overflow.js

@@ -2,7 +2,7 @@
  * http://creativecommons.org/publicdomain/zero/1.0/
  */
 
-async function testVal(aExpected, overflowSide = "") {
+async function testVal(aExpected, overflowSide = null) {
   info(`Testing ${aExpected}`);
   try {
     gURLBar.setURI(makeURI(aExpected));

browser/components/urlbar/tests/browser/browser_locationBarCommand.js

@@ -276,7 +276,7 @@ async function typeAndCommand(eventType, details = {}) {
 async function triggerCommand(eventType, details = {}) {
   Assert.equal(
     await UrlbarTestUtils.promiseUserContextId(window),
-    gBrowser.selectedTab.getAttribute("usercontextid"),
+    gBrowser.selectedTab.getAttribute("usercontextid") || "",
     "userContextId must be the same as the originating tab"
   );
 

devtools/client/framework/test/browser_dynamic_tool_enabling.js

@@ -11,7 +11,7 @@ var gItemsToTest = {
 };
 
 function expectedAttributeValueFromPrefs(prefs) {
-  return prefs.every(pref => Services.prefs.getBoolPref(pref)) ? "" : "true";
+  return prefs.every(pref => Services.prefs.getBoolPref(pref)) ? null : "true";
 }
 
 function checkItem(el, prefs) {

devtools/client/framework/test/browser_toolbox_remoteness_change.js

@@ -19,7 +19,7 @@ add_task(async function () {
   );
   is(
     tab.linkedBrowser.getAttribute("remote"),
-    "",
+    null,
     "And running in parent process"
   );
 

devtools/client/inspector/computed/test/browser_computed_search-filter_context-menu.js

@@ -88,12 +88,12 @@ add_task(async function () {
   cmdCopy = searchContextMenu.querySelector("#editmenu-copy");
   cmdPaste = searchContextMenu.querySelector("#editmenu-paste");
 
-  is(cmdUndo.getAttribute("disabled"), "", "cmdUndo is enabled");
+  is(cmdUndo.getAttribute("disabled"), null, "cmdUndo is enabled");
-  is(cmdDelete.getAttribute("disabled"), "", "cmdDelete is enabled");
+  is(cmdDelete.getAttribute("disabled"), null, "cmdDelete is enabled");
-  is(cmdSelectAll.getAttribute("disabled"), "", "cmdSelectAll is enabled");
+  is(cmdSelectAll.getAttribute("disabled"), null, "cmdSelectAll is enabled");
-  is(cmdCut.getAttribute("disabled"), "", "cmdCut is enabled");
+  is(cmdCut.getAttribute("disabled"), null, "cmdCut is enabled");
-  is(cmdCopy.getAttribute("disabled"), "", "cmdCopy is enabled");
+  is(cmdCopy.getAttribute("disabled"), null, "cmdCopy is enabled");
-  is(cmdPaste.getAttribute("disabled"), "", "cmdPaste is enabled");
+  is(cmdPaste.getAttribute("disabled"), null, "cmdPaste is enabled");
 
   onContextMenuClose = toolbox.once("menu-close");
   searchContextMenu.hidePopup();

devtools/client/inspector/rules/test/browser_rules_search-filter_context-menu.js

@@ -86,12 +86,12 @@ add_task(async function () {
   cmdCopy = searchContextMenu.querySelector("#editmenu-copy");
   cmdPaste = searchContextMenu.querySelector("#editmenu-paste");
 
-  is(cmdUndo.getAttribute("disabled"), "", "cmdUndo is enabled");
+  is(cmdUndo.getAttribute("disabled"), null, "cmdUndo is enabled");
-  is(cmdDelete.getAttribute("disabled"), "", "cmdDelete is enabled");
+  is(cmdDelete.getAttribute("disabled"), null, "cmdDelete is enabled");
-  is(cmdSelectAll.getAttribute("disabled"), "", "cmdSelectAll is enabled");
+  is(cmdSelectAll.getAttribute("disabled"), null, "cmdSelectAll is enabled");
-  is(cmdCut.getAttribute("disabled"), "", "cmdCut is enabled");
+  is(cmdCut.getAttribute("disabled"), null, "cmdCut is enabled");
-  is(cmdCopy.getAttribute("disabled"), "", "cmdCopy is enabled");
+  is(cmdCopy.getAttribute("disabled"), null, "cmdCopy is enabled");
-  is(cmdPaste.getAttribute("disabled"), "", "cmdPaste is enabled");
+  is(cmdPaste.getAttribute("disabled"), null, "cmdPaste is enabled");
 
   const onContextMenuHidden = toolbox.once("menu-close");
   searchContextMenu.hidePopup();

devtools/client/inspector/test/browser_inspector_search-filter_context-menu.js

@@ -96,12 +96,12 @@ add_task(async function () {
   cmdCopy = searchContextMenu.querySelector("#editmenu-copy");
   cmdPaste = searchContextMenu.querySelector("#editmenu-paste");
 
-  is(cmdUndo.getAttribute("disabled"), "", "cmdUndo is enabled");
+  is(cmdUndo.getAttribute("disabled"), null, "cmdUndo is enabled");
-  is(cmdDelete.getAttribute("disabled"), "", "cmdDelete is enabled");
+  is(cmdDelete.getAttribute("disabled"), null, "cmdDelete is enabled");
-  is(cmdSelectAll.getAttribute("disabled"), "", "cmdSelectAll is enabled");
+  is(cmdSelectAll.getAttribute("disabled"), null, "cmdSelectAll is enabled");
-  is(cmdCut.getAttribute("disabled"), "", "cmdCut is enabled");
+  is(cmdCut.getAttribute("disabled"), null, "cmdCut is enabled");
-  is(cmdCopy.getAttribute("disabled"), "", "cmdCopy is enabled");
+  is(cmdCopy.getAttribute("disabled"), null, "cmdCopy is enabled");
-  is(cmdPaste.getAttribute("disabled"), "", "cmdPaste is enabled");
+  is(cmdPaste.getAttribute("disabled"), null, "cmdPaste is enabled");
 
   const onContextMenuHidden = toolbox.once("menu-close");
   searchContextMenu.hidePopup();

devtools/client/webconsole/test/browser/browser_jsterm_editor_reverse_search_keyboard_navigation.js

@@ -42,7 +42,7 @@ add_task(async function () {
   await wait(1000);
   is(
     readerModeButtonEl.getAttribute("readeractive"),
-    "",
+    null,
     "reader mode wasn't activated"
   );
 
@@ -72,7 +72,7 @@ add_task(async function () {
   await wait(1000);
   is(
     readerModeButtonEl.getAttribute("readeractive"),
-    "",
+    null,
     "reader mode still wasn't activated"
   );
 

dom/base/Element.cpp

@@ -1460,13 +1460,7 @@ void Element::GetAttribute(const nsAString& aName, DOMString& aReturn) {
   if (val) {
     val->ToString(aReturn);
   } else {
-    if (IsXULElement()) {
+    aReturn.SetNull();
-      // XXX should be SetDOMStringToNull(aReturn);
-      // See bug 232598
-      // aReturn is already empty
-    } else {
-      aReturn.SetNull();
-    }
   }
 }
 

dom/base/test/test_bug564863-2.xhtml

@@ -55,11 +55,11 @@ SimpleTest.waitForExplicitFinish();
     // not when run as a Mochitest plain.
     //is(xul_cs.color, "rgb(0, 0, 0)", "xul color " + test);
 
-    attrValue = removed ? null : "";
+    let attrValue = removed ? null : "";
 
     is(xul.id, "", "xul id " + test);
 
-    is(xul.getAttribute("id"), "",        "xul getAttribute " + test);
+    is(xul.getAttribute("id"), attrValue, "xul getAttribute " + test);
 
     is($("xul_id"), null, "xul getElementById " + test);
   }
@@ -149,7 +149,7 @@ SimpleTest.waitForExplicitFinish();
   await new Promise(SimpleTest.executeSoon);
   if (mutation) {
     is(mutation.target, xul, "target is xul");
-    is(xul.getAttribute("id"), "", "xul no longer has id attr");
+    is(xul.getAttribute("id"), null, "xul no longer has id attr");
     is(xul.id, "", "xul no longer has id");
     xul.id = "other_xul_id";
   } else {

dom/ipc/tests/JSWindowActor/browser_event_listener.js

@@ -144,7 +144,7 @@ declTest("test in-process content events are not processed twice", {
       "content",
       "Should be a content <browser>"
     );
-    is(browser.getAttribute("remotetype"), "", "Should not be remote");
+    is(browser.getAttribute("remotetype"), null, "Should not be remote");
     await testEventProcessedOnce(browser);
   },
 });
@@ -160,8 +160,12 @@ declTest("test in-process chrome events are processed correctly", {
       "chrome://mochitests/content/browser/dom/ipc/tests/JSWindowActor/file_dummyChromePage.html"
     );
     let chromeBrowser = dialog._frame;
-    is(chromeBrowser.getAttribute("type"), "", "Should be a chrome <browser>");
+    is(
-    is(chromeBrowser.getAttribute("remotetype"), "", "Should not be remote");
+      chromeBrowser.getAttribute("type"),
+      null,
+      "Should be a chrome <browser>"
+    );
+    is(chromeBrowser.getAttribute("remotetype"), null, "Should not be remote");
 
     await testEventProcessedOnce(chromeBrowser, "dummyChromePage.html");
 

dom/tests/mochitest/webcomponents/test_xul_custom_element.xhtml

@@ -150,13 +150,13 @@
     function basicElementCreateBuiltIn() {
       let element = document.createElementNS(XUL_NS, "axulelement", { is: "test-built-in-element" });
       ok(element instanceof TestCustomBuiltInElement, "Should be an instance of TestCustomBuiltInElement");
-      is(element.getAttribute("is"), "", "The |is| attribute of the created element should not be the extended type.");
+      is(element.getAttribute("is"), null, "The |is| attribute of the created element should not be the extended type.");
       document.querySelector("#content").appendChild(element);
       is(element.textContent, "baz", "Should have set the textContent");
 
       let element2 = element.cloneNode(false);
       is(element2.localName, "axulelement", "Should see the right tag");
-      is(element2.getAttribute("is"), "", "The |is| attribute of the created element should not be the extended type.");
+      is(element2.getAttribute("is"), null, "The |is| attribute of the created element should not be the extended type.");
       is(element2.textContent, "", "Shouldn't have cloned the textContent");
       document.querySelector("#content").appendChild(element2);
       is(element2.textContent, "baz", "Should have set the textContent");
@@ -188,13 +188,13 @@
     function subclassElementCreateBuiltIn() {
       let element = document.createElementNS(XUL_NS, "menupopup", { is: "test-popup-extend" });
       ok(element instanceof TestPopupExtendElement, "Should be an instance of TestPopupExtendElement");
-      is(element.getAttribute("is"), "", "The |is| attribute of the created element should not be the extended type.");
+      is(element.getAttribute("is"), null, "The |is| attribute of the created element should not be the extended type.");
       document.querySelector("#content").appendChild(element);
       is(element.textContent, "quuz", "Should have set the textContent");
 
       let element2 = element.cloneNode(false);
       is(element2.localName, "menupopup", "Should see the right tag");
-      is(element2.getAttribute("is"), "", "The |is| attribute of the created element should not be the extended type.");
+      is(element2.getAttribute("is"), null, "The |is| attribute of the created element should not be the extended type.");
       is(element2.textContent, "", "Shouldn't have cloned the textContent");
       document.querySelector("#content").appendChild(element2);
       is(element2.textContent, "quuz", "Should have set the textContent");
@@ -268,13 +268,13 @@
       let element = document.createElementNS(XUL_NS, "testwithoutdash", { is: "testwithoutdash-extended" });
       ok(element instanceof TestWithoutDashExtended, "Should be an instance of TestWithoutDashExtended");
       ok(element instanceof TestWithoutDash, "Should be an instance of TestWithoutDash");
-      is(element.getAttribute("is"), "", "The |is| attribute of the created element should not be the extended type.");
+      is(element.getAttribute("is"), null, "The |is| attribute of the created element should not be the extended type.");
       document.querySelector("#content").appendChild(element);
       is(element.textContent, "quux", "Should have set the textContent");
 
       let element2 = element.cloneNode(false);
       is(element2.localName, "testwithoutdash", "Should see the right tag");
-      is(element2.getAttribute("is"), "", "The |is| attribute of the created element should not be the extended type.");
+      is(element2.getAttribute("is"), null, "The |is| attribute of the created element should not be the extended type.");
       is(element2.textContent, "", "Shouldn't have cloned the textContent");
       document.querySelector("#content").appendChild(element2);
       is(element2.textContent, "quux", "Should have set the textContent");

security/manager/ssl/tests/mochitest/browser/browser_loadPKCS11Module_ui.js

@@ -290,7 +290,7 @@ async function testModuleNameHelper(moduleName, acceptButtonShouldBeDisabled) {
   let dialogNode = win.document.querySelector("dialog");
   Assert.equal(
     dialogNode.getAttribute("buttondisabledaccept"),
-    acceptButtonShouldBeDisabled ? "true" : "", // it's a string
+    acceptButtonShouldBeDisabled ? "true" : null,
     `dialog accept button should ${
       acceptButtonShouldBeDisabled ? "" : "not "
     }be disabled`

toolkit/components/passwordmgr/test/browser/browser_doorhanger_form_password_edit.js

@@ -30,7 +30,7 @@ let testCases = [
       doorhanger: {
         type: "password-save",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "",
         password: "abcXYZ",
         toggle: "visible",
@@ -56,7 +56,7 @@ let testCases = [
       doorhanger: {
         type: "password-save",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "",
         password: "pass-changed",
         toggle: "visible",
@@ -80,7 +80,7 @@ let testCases = [
       doorhanger: {
         type: "password-change",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "user1",
         password: "autopass-changed",
       },
@@ -104,7 +104,7 @@ let testCases = [
       doorhanger: {
         type: "password-save",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "user2",
         password: "pass2",
         toggle: "visible",
@@ -147,7 +147,7 @@ let testCases = [
       doorhanger: {
         type: "password-save",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "user2",
         password: "pass1",
         toggle: "visible",
@@ -174,7 +174,7 @@ let testCases = [
       doorhanger: {
         type: "password-change",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "user-saved",
         password: "pass2",
         toggle: "visible",
@@ -198,7 +198,7 @@ let testCases = [
       doorhanger: {
         type: "password-change",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "user1",
         password: "pass1",
         toggle: "visible",
@@ -244,7 +244,7 @@ let testCases = [
       doorhanger: {
         type: "password-save",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "",
         password: "a",
         toggle: "visible",
@@ -271,7 +271,7 @@ let testCases = [
       doorhanger: {
         type: "password-save",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "",
         password: "abc",
         toggle: "visible",
@@ -296,7 +296,7 @@ let testCases = [
       doorhanger: {
         type: "password-change",
         dismissed: true,
-        anchorExtraAttr: "",
+        anchorExtraAttr: null,
         username: "",
         password: "pass",
         toggle: "visible",

toolkit/components/pdfjs/test/browser_pdfjs_editing_contextmenu.js

@@ -130,7 +130,7 @@ function assertMenuitems(menuitems, expected) {
         elmt =>
           !elmt.id.includes("-sep-") &&
           !elmt.hidden &&
-          ["", "false"].includes(elmt.getAttribute("disabled"))
+          [null, "false"].includes(elmt.getAttribute("disabled"))
       )
       .map(elmt => elmt.id),
     expected

toolkit/components/tooltiptext/TooltipTextProvider.sys.mjs

@@ -69,11 +69,7 @@ TooltipTextProvider.prototype = {
       }
       if (tipElement.namespaceURI == XUL_NS) {
         lookingForSVGTitle = false;
-        // NOTE: getAttribute behaves differently for XUL so we can't rely on
+        titleText = tipElement.getAttribute("tooltiptext");
-        // it returning null, see bug 232598.
-        titleText = tipElement.hasAttribute("tooltiptext")
-          ? tipElement.getAttribute("tooltiptext")
-          : null;
       } else if (!defView.SVGElement.isInstance(tipElement)) {
         lookingForSVGTitle = false;
         titleText = tipElement.getAttribute("title");

toolkit/components/xulstore/XULStore.sys.mjs

@@ -153,7 +153,7 @@ XULStore.prototype = {
     }
 
     const uri = node.ownerDocument.documentURI;
-    const value = node.getAttribute(attr);
+    const value = node.getAttribute(attr) || "";
 
     if (node.localName == "window") {
       this.log("Persisting attributes to windows is handled by AppWindow.");

toolkit/content/customElements.js

@@ -732,7 +732,7 @@
       }
 
       get label() {
-        return this.getAttribute("label");
+        return this.getAttribute("label") || "";
       }
 
       set image(val) {
@@ -762,9 +762,7 @@
       }
 
       get accessKey() {
-        return this.labelElement
+        return this.labelElement?.accessKey || this.getAttribute("accesskey");
-          ? this.labelElement.accessKey
-          : this.getAttribute("accesskey");
       }
     };
   MozElements.BaseTextMixin = BaseTextMixin;

toolkit/content/tests/chrome/test_labelcontrol.xhtml

@@ -40,7 +40,7 @@ function runTests()
   let checkboxLabel = $("checkbox-label");
   is(checkboxLabel.control, "checkbox", "checkbox control");
   is(checkboxLabel.labeledControlElement, checkbox, "checkbox labeledControlElement");
-  is(checkbox.accessKey, "", "checkbox accessKey not set");
+  is(checkbox.accessKey, null, "checkbox accessKey not set");
   checkboxLabel.accessKey = "C";
   is(checkbox.accessKey, "C", "checkbox accessKey set");
 

toolkit/content/tests/chrome/test_menuitem_commands.xhtml

@@ -49,10 +49,10 @@ function runTestSet(suffix)
   var three = $("three" + suffix);
   var four = $("four" + suffix);
 
-  checkAttributes(one, "One", "", "", true, false);
+  checkAttributes(one, "One", null, null, true, false);
-  checkAttributes(two, "", "", "false", false, false);
+  checkAttributes(two, null, null, "false", false, false);
   checkAttributes(three, "Three", "T", "true", false, false);
-  checkAttributes(four, "Four", "F", "", false, false);
+  checkAttributes(four, "Four", "F", null, false, false);
 
   if (isMac && suffix) {
     var utils = window.windowUtils;
@@ -62,8 +62,8 @@ function runTestSet(suffix)
     $("menu" + suffix).open = true;
   }
 
-  checkAttributes(one, "One", "", "", false, true);
+  checkAttributes(one, "One", null, null, false, true);
-  checkAttributes(two, "Cat", "C", "", false, true);
+  checkAttributes(two, "Cat", "C", null, false, true);
   checkAttributes(three, "Dog", "D", "false", true, true);
   checkAttributes(four, "Four", "F", "true", false, true);
 

toolkit/content/tests/chrome/test_menulist_null_value.xhtml

@@ -34,7 +34,7 @@ function runTests()
 
   list.selectedItem = null;
   is(list.value, "", "Check list value after setting selectedItem to null");
-  is(list.getAttribute("label"), "", "Check list label after setting selectedItem to null");
+  is(list.getAttribute("label"), null, "Check list label after setting selectedItem to null");
 
   // select something again to make sure the label is not already empty
   list.selectedIndex = 1;
@@ -61,14 +61,14 @@ function runTests()
   // set the value to null and test it (bug 408940)
   list.value = null;
   is(list.value, "", "Check list value after setting value to null");
-  is(list.getAttribute("label"), "", "Check list label after setting value to null");
+  is(list.getAttribute("label"), null, "Check list label after setting value to null");
 
   // select something again to make sure the label is not already empty
   list.selectedIndex = 1;
   // set the value to undefined and test it (bug 408940)
   list.value = undefined;
   is(list.value, "", "Check list value after setting value to undefined");
-  is(list.getAttribute("label"), "", "Check list label after setting value to undefined");
+  is(list.getAttribute("label"), null, "Check list label after setting value to undefined");
 
   // select something again to make sure the label is not already empty
   list.selectedIndex = 1;
@@ -76,7 +76,7 @@ function runTests()
   // and make sure the previous label is removed
   list.value = "this does not exist";
   is(list.value, "this does not exist", "Check the list value after setting it to something not associated witn an existing menuitem");
-  is(list.getAttribute("label"), "", "Check that the list label is empty after selecting a nonexistent item");
+  is(list.getAttribute("label"), null, "Check that the list label is empty after selecting a nonexistent item");
 
   SimpleTest.finish();
 }

toolkit/content/tests/chrome/window_chromemargin.xhtml

@@ -16,15 +16,19 @@ function ok(condition, message) {
   window.arguments[0].SimpleTest.ok(condition, message);
 }
 
+function is(a, b, message) {
+  window.arguments[0].SimpleTest.is(a, b, message);
+}
+
 function doSingleTest(param)
 {
   var exception = null;
   try {
     document.documentElement.removeAttribute("chromemargin");
     document.documentElement.setAttribute("chromemargin", param);
-    ok(document.
+    is(document.
        documentElement.
-       getAttribute("chromemargin") == param, "couldn't set/get chromemargin?");
+       getAttribute("chromemargin"), param, "couldn't set/get chromemargin?");
   } catch (ex) {
     exception = ex;
   }
@@ -44,7 +48,7 @@ function runTests()
 
   // test remove
   doc.removeAttribute("chromemargin");
-  ok(doc.getAttribute("chromemargin") == "", "couldn't remove chromemargin?");
+  is(doc.getAttribute("chromemargin"), null, "couldn't remove chromemargin?");
 
   // we already test these really well in a c++ test in widget
   doSingleTest("1,2,3,4");

toolkit/content/tests/chrome/window_keys.xhtml

@@ -82,7 +82,7 @@ function runTest()
   document.documentElement.appendChild(keyset);
   iterateKeys(true, "appended");
 
-  var accelText = menuitem => menuitem.getAttribute("acceltext").toLowerCase();
+  var accelText = menuitem => (menuitem.getAttribute("acceltext") || "").toLowerCase();
 
   $("menubutton").open = true;
 

toolkit/content/tests/chrome/window_largemenu.xhtml

@@ -363,8 +363,8 @@ function testPopupMovement()
   is(screenX, expectedx, gTests[gTestIndex] + " (6000, 100) x");
   is(screenY, 100, gTests[gTestIndex] + " (6000, 100) y");
 
-  is(popup.getAttribute("left"), "", gTests[gTestIndex] + " left is empty after moving");
+  is(popup.getAttribute("left"), null, gTests[gTestIndex] + " left is empty after moving");
-  is(popup.getAttribute("top"), "", gTests[gTestIndex] + " top is empty after moving");
+  is(popup.getAttribute("top"), null, gTests[gTestIndex] + " top is empty after moving");
   popup.setAttribute("left", "80");
   popup.setAttribute("top", "82");
   [screenX, screenY] = getScreenXY(popup);
@@ -387,8 +387,8 @@ function testPopupMovement()
 
   is(screenX, expectedx, gTests[gTestIndex] + " move after set left and top x to -1");
   is(screenY, expectedy, gTests[gTestIndex] + " move after set left and top y to -1");
-  is(popup.getAttribute("left"), "", gTests[gTestIndex] + " left is not set after moving to -1");
+  is(popup.getAttribute("left"), null, gTests[gTestIndex] + " left is not set after moving to -1");
-  is(popup.getAttribute("top"), "", gTests[gTestIndex] + " top is not set after moving to -1");
+  is(popup.getAttribute("top"), null, gTests[gTestIndex] + " top is not set after moving to -1");
 
   popup.hidePopup();
 }

toolkit/content/tests/widgets/tree_shared.js

@@ -321,11 +321,7 @@ function testtag_tree_columns(tree, expectedColumns, testid) {
     // check the view's getColumnProperties method
     var properties = tree.view.getColumnProperties(column);
     var expectedProperties = expectedColumn.properties;
-    is(
+    is(properties, expectedProperties || "", adjtestid + "getColumnProperties");
-      properties,
-      expectedProperties ? expectedProperties : "",
-      adjtestid + "getColumnProperties"
-    );
   }
 
   is(columns.getFirstColumn(), columns[0], testid + "getFirstColumn");
@@ -2151,12 +2147,12 @@ function convertDOMtoTreeRowInfo(treechildren, level, rowidx) {
       for (var c = 0; c < treerow.childNodes.length; c++) {
         var cell = treerow.childNodes[c];
         cellInfo.push({
-          label: "" + cell.getAttribute("label"),
+          label: cell.getAttribute("label") || "",
-          value: cell.getAttribute("value"),
+          value: cell.getAttribute("value") || "",
-          properties: cell.getAttribute("properties"),
+          properties: cell.getAttribute("properties") || "",
           editable: cell.getAttribute("editable") != "false",
           selectable: cell.getAttribute("selectable") != "false",
-          image: cell.getAttribute("src"),
+          image: cell.getAttribute("src") || "",
           mode: cell.hasAttribute("mode")
             ? parseInt(cell.getAttribute("mode"))
             : 3,
@@ -2170,7 +2166,7 @@ function convertDOMtoTreeRowInfo(treechildren, level, rowidx) {
           : convertDOMtoTreeRowInfo(descendants, level + 1, rowidx);
       obj.rows.push({
         cells: cellInfo,
-        properties: treerow.getAttribute("properties"),
+        properties: treerow.getAttribute("properties") || "",
         container: treeitem.getAttribute("container") == "true",
         separator: treeitem.localName == "treeseparator",
         children,

toolkit/content/widgets/button.js

@@ -84,7 +84,7 @@
         ).toLowerCase();
 
         // If the accesskey of the current button is pressed, just activate it
-        if (this.accessKey.toLowerCase() == charPressedLower) {
+        if (this.accessKey?.toLowerCase() == charPressedLower) {
           this.click();
           return;
         }
@@ -201,7 +201,7 @@
       while (iterator.nextNode()) {
         var test = iterator.currentNode;
         if (
-          test.accessKey.toLowerCase() == aAccessKeyLower &&
+          test.accessKey?.toLowerCase() == aAccessKeyLower &&
           !test.disabled &&
           !test.collapsed &&
           !test.hidden

toolkit/content/widgets/menu.js

@@ -19,7 +19,7 @@
         this.setAttribute("value", val);
       }
       get value() {
-        return this.getAttribute("value");
+        return this.getAttribute("value") || "";
       }
 
       // nsIDOMXULSelectControlItemElement

toolkit/content/widgets/menulist.js

@@ -153,7 +153,7 @@
 
     // nsIDOMXULSelectControlElement
     get value() {
-      return this.getAttribute("value");
+      return this.getAttribute("value") || "";
     }
 
     // nsIDOMXULMenuListElement
@@ -163,12 +163,12 @@
 
     // nsIDOMXULMenuListElement
     get image() {
-      return this.getAttribute("image");
+      return this.getAttribute("image") || "";
     }
 
     // nsIDOMXULMenuListElement
     get label() {
-      return this.getAttribute("label");
+      return this.getAttribute("label") || "";
     }
 
     set description(val) {
@@ -176,7 +176,7 @@
     }
 
     get description() {
-      return this.getAttribute("description");
+      return this.getAttribute("description") || "";
     }
 
     // nsIDOMXULMenuListElement

toolkit/content/widgets/radio.js

@@ -214,7 +214,7 @@
     }
 
     get value() {
-      return this.getAttribute("value");
+      return this.getAttribute("value") || "";
     }
 
     set disabled(val) {
@@ -526,7 +526,7 @@
     }
 
     get value() {
-      return this.getAttribute("value");
+      return this.getAttribute("value") || "";
     }
 
     get selected() {

toolkit/content/widgets/richlistbox.js

@@ -116,7 +116,7 @@
           var searchText =
             "searchLabel" in listitem
               ? listitem.searchLabel
-              : listitem.getAttribute("label"); // (see also bug 250123)
+              : listitem.getAttribute("label") || ""; // (see also bug 250123)
           searchText = searchText.substring(0, length).toLowerCase();
           if (searchText == incrementalString) {
             this.ensureIndexIsVisible(k);
@@ -227,7 +227,7 @@
       this.setAttribute("seltype", val);
     }
     get selType() {
-      return this.getAttribute("seltype");
+      return this.getAttribute("seltype") || "";
     }
 
     // nsIDOMXULSelectControlElement
@@ -977,7 +977,7 @@
     }
 
     get value() {
-      return this.getAttribute("value");
+      return this.getAttribute("value") || "";
     }
 
     /**

toolkit/content/widgets/tabbox.js

@@ -459,7 +459,7 @@
     }
 
     get value() {
-      return this.getAttribute("value");
+      return this.getAttribute("value") || "";
     }
 
     get control() {
@@ -563,7 +563,7 @@
     }
 
     get value() {
-      return this.getAttribute("value");
+      return this.getAttribute("value") || "";
     }
 
     get tabbox() {

toolkit/content/widgets/tree.js

@@ -1078,7 +1078,7 @@
     }
 
     get selType() {
-      return this.getAttribute("seltype");
+      return this.getAttribute("seltype") || "";
     }
 
     set currentIndex(val) {

toolkit/modules/ShortcutUtils.sys.mjs

@@ -56,9 +56,12 @@ export var ShortcutUtils = {
   },
 
   getModifierString(elemMod) {
+    if (!elemMod) {
+      return "";
+    }
+
     let elemString = "";
     let haveCloverLeaf = false;
-
     if (elemMod.match("accel")) {
       if (Services.appinfo.OS == "Darwin") {
         haveCloverLeaf = true;

toolkit/mozapps/update/tests/browser/browser_doorhanger_bc_multiUpdate.js

@@ -64,7 +64,7 @@ add_task(async function doorhanger_bc_multiUpdate() {
 
       is(
         PanelUI.menuButton.getAttribute("badge-status"),
-        "",
+        null,
         "Should not have restart badge during staging"
       );
 

toolkit/mozapps/update/tests/browser/browser_doorhanger_bc_multiUpdate_promptWaitTime.js

@@ -74,7 +74,7 @@ add_task(async function doorhanger_bc_multiUpdate() {
 
       is(
         PanelUI.menuButton.getAttribute("badge-status"),
-        "",
+        null,
         "Should not have restart badge during staging"
       );