Bug 1731668 - Move downloads spam prevention work behind a pref. r=mhowell

Differential Revision: https://phabricator.services.mozilla.com/D126296

modules/libpref/init/StaticPrefList.yaml

@@ -1119,6 +1119,12 @@
   value: false
   mirror: always
 
+# See bug 1731668
+- name: browser.download.enable_spam_prevention
+  type: bool
+  value: false
+  mirror: always
+
 - name: browser.download.sanitize_non_media_extensions
   type: bool
   value: true

uriloader/exthandler/nsExternalHelperAppService.cpp

@@ -1683,7 +1683,7 @@ NS_IMETHODIMP nsExternalAppHandler::OnStartRequest(nsIRequest* request) {
     aChannel->GetURI(getter_AddRefs(mSourceUrl));
   }
 
-  if (StaticPrefs::browser_download_improvements_to_download_panel() &&
+  if (StaticPrefs::browser_download_enable_spam_prevention() &&
       IsDownloadSpam(aChannel)) {
     return NS_OK;
   }

uriloader/exthandler/tests/mochitest/browser_download_spam_permissions.js

@@ -30,7 +30,13 @@ add_task(async function setup() {
     Services.perms.UNKNOWN
   );
   await SpecialPowers.pushPrefEnv({
-    set: [["browser.download.improvements_to_download_panel", true]],
+    set: [
+      // We enable browser.download.improvements_to_download_panel here since
+      // the test expects the download to be saved directly to disk and not
+      // prompted by the UnknownContentType window.
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.enable_spam_prevention", true],
+    ],
   });
 
   registerCleanupFunction(async () => {