Merging upstream version 126.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

65 files changed, 416 insertions, 214 deletions

diff --git a/toolkit/content/tests/browser/browser_about_logging.js b/toolkit/content/tests/browser/browser_about_logging.js
index fdf8eab57b..d9a2459c12 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 ffbc916a5e..9b6f636db3 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 be6ae7d1f7..c0413c459b 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 21b22fe171..3473dfc915 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 7c40b5fe1a..9e18cc89f3 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 073e71a88b..6bcc95ae65 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 3f3e729dab..b028cac4ae 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 f4afa44903..0240d9c14b 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 46e2c78af5..532f7743b2 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 be15cd9684..03a239463d 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 b124361fd7..74846e3c27 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 698d26b43a..ee595706f5 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/chrome.toml b/toolkit/content/tests/chrome/chrome.toml
index 3391a2923d..986822ac48 100644
--- a/toolkit/content/tests/chrome/chrome.toml
+++ b/toolkit/content/tests/chrome/chrome.toml
@@ -226,6 +226,8 @@ support-files = [
 
 ["test_menulist_initial_selection.xhtml"]
 
+["test_menulist_initial_selection_with_connected_callback.xhtml"]
+
 ["test_menulist_keynav.xhtml"]
 
 ["test_menulist_null_value.xhtml"]
diff --git a/toolkit/content/tests/chrome/file_editor_with_autocomplete.js b/toolkit/content/tests/chrome/file_editor_with_autocomplete.js
index 78611efc70..acf2c9e9df 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 003af044e5..71846a01ea 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 cd8d312e1d..f9f8a0eaf5 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_labelcontrol.xhtml b/toolkit/content/tests/chrome/test_labelcontrol.xhtml
index 06e7f96105..937d3e7403 100644
--- a/toolkit/content/tests/chrome/test_labelcontrol.xhtml
+++ b/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");
 
diff --git a/toolkit/content/tests/chrome/test_menuitem_blink.xhtml b/toolkit/content/tests/chrome/test_menuitem_blink.xhtml
index 700a8a7465..ad76eee8bf 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_menuitem_commands.xhtml b/toolkit/content/tests/chrome/test_menuitem_commands.xhtml
index 60a35b36c5..a342b9d1d5 100644
--- a/toolkit/content/tests/chrome/test_menuitem_commands.xhtml
+++ b/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(two, "", "", "false", false, false);
+  checkAttributes(one, "One", null, null, true, 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(two, "Cat", "C", "", false, true);
+  checkAttributes(one, "One", null, null, false, true);
+  checkAttributes(two, "Cat", "C", null, false, true);
   checkAttributes(three, "Dog", "D", "false", true, true);
   checkAttributes(four, "Four", "F", "true", false, true);
 
diff --git a/toolkit/content/tests/chrome/test_menulist_in_popup.xhtml b/toolkit/content/tests/chrome/test_menulist_in_popup.xhtml
index 971fe90322..75fb19adcf 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_menulist_initial_selection.xhtml b/toolkit/content/tests/chrome/test_menulist_initial_selection.xhtml
index 19e9beae67..255318f5a7 100644
--- a/toolkit/content/tests/chrome/test_menulist_initial_selection.xhtml
+++ b/toolkit/content/tests/chrome/test_menulist_initial_selection.xhtml
@@ -29,6 +29,9 @@ async function runTest() {
   is(menulist2.value, "", "menulist2 should not be selected to the first item's value");
   is(menulist2.label, "None", "menulist2 should not be selected to the first item's value");
 
+  is(menulist1.menupopup.querySelectorAll('menuitem[selected="true"]').length, 1, "menulist1 should have only one selected item.");
+  is(menulist2.menupopup.querySelectorAll('menuitem[selected="true"]').length, 0, "menulist2 should have no selected items.");
+
   SimpleTest.finish();
 }
 
@@ -37,17 +40,17 @@ async function runTest() {
 
 <panel>
   <menulist id="menulist1" value="" label="None">
-    <menupopup id="menulistpopup">
+    <menupopup id="menulistpopup1">
       <menuitem value="1" label="One"/>
       <menuitem value="2" label="Two"/>
       <menuitem value="3" label="Three"/>
     </menupopup>
   </menulist>
   <menulist id="menulist2" value="" label="None" noinitialselection="true">
-    <menupopup id="menulistpopup">
-      <menuitem value="1" label="One"/>
-      <menuitem value="2" label="Two"/>
-      <menuitem value="3" label="Three"/>
+    <menupopup id="menulistpopup2">
+      <menuitem value="4" label="Four"/>
+      <menuitem value="5" label="Five"/>
+      <menuitem value="6" label="Six"/>
     </menupopup>
   </menulist>
 </panel>
diff --git a/toolkit/content/tests/chrome/test_menulist_initial_selection_with_connected_callback.xhtml b/toolkit/content/tests/chrome/test_menulist_initial_selection_with_connected_callback.xhtml
new file mode 100644
index 0000000000..2c9b462948
--- /dev/null
+++ b/toolkit/content/tests/chrome/test_menulist_initial_selection_with_connected_callback.xhtml
@@ -0,0 +1,80 @@
+<window title="Menulist Initial Selection Connected Callback Test"
+        onload="setTimeout(runTest, 0)"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"></script>
+<script>
+<![CDATA[
+SimpleTest.waitForExplicitFinish();
+
+async function runTest() {
+  const panel = document.querySelector("panel");
+
+  // Dynamically initialize two menulists, one with the noinitialselection
+  // attribute and one without, but ensure that their delayConnectedCallback
+  // functions always return true to ensure that connectedCallback will not run yet.
+  const menulist1 = document.createXULElement("menulist");
+  menulist1.delayConnectedCallback = () => true;
+  menulist1.setAttribute("id", "menulist1");
+  menulist1.appendItem(/* label */ "One",   /* id */ "1");
+  menulist1.appendItem(/* label */ "Two",   /* id */ "2");
+  menulist1.appendItem(/* label */ "Three", /* id */ "3");
+  is(menulist1.menupopup.querySelectorAll('menuitem[selected="true"]').length, 0, "menulist1 should have no selected items yet.");
+
+  const menulist2 = document.createXULElement("menulist");
+  menulist2.delayConnectedCallback = () => true;
+  menulist2.setAttribute("id", "menulist2");
+  menulist2.setAttribute("noinitialselection", "true");
+  menulist2.appendItem(/* label */ "Four", /* id */ "4");
+  menulist2.appendItem(/* label */ "Five", /* id */ "5");
+  menulist2.appendItem(/* label */ "Six",  /* id */ "6");
+  is(menulist2.menupopup.querySelectorAll('menuitem[selected="true"]').length, 0, "menulist2 should have no selected items yet.");
+
+  // Set their values before allowing connectedCallback to run, simulating
+  // a race condition where an initial value is manually set before the
+  // connectedCallback is invoked.
+  menulist1.value = "2";
+  panel.appendChild(menulist1);
+  menulist1.delayConnectedCallback = () => false;
+  menulist1.connectedCallback();
+
+  menulist2.value = "5";
+  panel.appendChild(menulist2);
+  menulist2.delayConnectedCallback = () => false;
+  menulist2.connectedCallback();
+
+  const panelShown = new Promise(r => panel.addEventListener("popupshown", r, { once: true }));
+  info("opening panel");
+  panel.openPopup(null, { x: 0, y: 0 });
+  await panelShown;
+  info("panel opened");
+
+  is(menulist1.value, "2", "menulist1 should have the second menuitem's value");
+  is(menulist1.label, "Two", "menulist1 should have the second menuitem's label");
+  is(menulist1.menupopup.querySelectorAll('menuitem[selected="true"]').length, 1, "menulist1 should have only one selected item.");
+
+  is(menulist2.value, "5", "menulist2 should not be selected to the second item's value");
+  is(menulist2.label, "Five", "menulist2 should not be selected to the second item's value");
+  is(menulist2.menupopup.querySelectorAll('menuitem[selected="true"]').length, 1, "menulist2 should have only one selected item.");
+
+  menulist1.value = "3";
+  menulist2.value = "6";
+
+  is(menulist1.value, "3", "menulist1 should have the third menuitem's value");
+  is(menulist1.label, "Three", "menulist1 should have the third menuitem's label");
+  is(menulist1.menupopup.querySelectorAll('menuitem[selected="true"]').length, 1, "menulist1 should have only one selected item.");
+
+  is(menulist2.value, "6", "menulist2 should not be selected to the third item's value");
+  is(menulist2.label, "Six", "menulist2 should not be selected to the third item's value");
+  is(menulist2.menupopup.querySelectorAll('menuitem[selected="true"]').length, 1, "menulist2 should have only one selected item.");
+
+  SimpleTest.finish();
+}
+
+]]>
+</script>
+<panel></panel>
+</window>
+
+
diff --git a/toolkit/content/tests/chrome/test_menulist_null_value.xhtml b/toolkit/content/tests/chrome/test_menulist_null_value.xhtml
index 9312c236dc..e0ef42f5bd 100644
--- a/toolkit/content/tests/chrome/test_menulist_null_value.xhtml
+++ b/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();
 }
diff --git a/toolkit/content/tests/chrome/test_notificationbox.xhtml b/toolkit/content/tests/chrome/test_notificationbox.xhtml
index 8de985175a..9a2bc9d888 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 6b8dd31143..e72c496a59 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 a7800caaad..628ff2a851 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_richlistbox.xhtml b/toolkit/content/tests/chrome/test_richlistbox.xhtml
index 48303e0172..65f3626a8c 100644
--- a/toolkit/content/tests/chrome/test_richlistbox.xhtml
+++ b/toolkit/content/tests/chrome/test_richlistbox.xhtml
@@ -5,7 +5,6 @@
   XUL Widget Test for listbox direction
   -->
 <window title="Listbox direction test"
-        onload="test_richlistbox()"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
   <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
   <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"></script>
@@ -26,8 +25,7 @@ function getScrollIndexAmount(aDirection) {
   return (4 * aDirection + richListBox.currentIndex);
 }
 
-function test_richlistbox()
-{
+add_task(function test_richlistbox() {
   var height = richListBox.clientHeight;
   var item;
   do {
@@ -93,9 +91,22 @@ function test_richlistbox()
   richListBox.selectedItem = richListBox.firstChild;
   richListBox.firstChild.nextSibling.setAttribute("disabled", true);
   richListBox.focus();
+
   synthesizeKey("KEY_ArrowDown", {}, window);
   is(richListBox.selectedItems.length, 1, "one item selected");
-  is(richListBox.selectedItems[0], richListBox.firstChild, "first item selected");
+  is(richListBox.selectedItems[0], richListBox.getItemAtIndex(2), "skipped over disabled item on keydown");
+
+  synthesizeKey("KEY_ArrowUp", {}, window);
+  is(richListBox.selectedItems.length, 1, "one item selected");
+  is(richListBox.selectedItems[0], richListBox.firstChild, "skipped over disabled item on keyup");
+
+  synthesizeMouseAtCenter(richListBox.getItemAtIndex(1), {});
+  is(richListBox.selectedItems.length, 1, "one item selected");
+  is(richListBox.selectedItems[0], richListBox.firstChild, "cannot select disabled item");
+
+  synthesizeMouseAtCenter(richListBox.getItemAtIndex(2), {});
+  is(richListBox.selectedItems.length, 1, "one item selected");
+  is(richListBox.selectedItems[0], richListBox.getItemAtIndex(2), "can select enabled item");
 
   // Selected item re-insertion should keep the item selected.
   richListBox.clearSelection();
@@ -107,9 +118,7 @@ function test_richlistbox()
   richListBox.append(item);
   is(richListBox.selectedItems.length, 1, "one item selected");
   is(richListBox.selectedItems[0], item, "last (previosly first) item selected");
-
-  SimpleTest.finish();
-}
+});
 
 ]]>
 </script>
diff --git a/toolkit/content/tests/chrome/test_tree_view.xhtml b/toolkit/content/tests/chrome/test_tree_view.xhtml
index 5e45161c6c..c9ec889995 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_chromemargin.xhtml b/toolkit/content/tests/chrome/window_chromemargin.xhtml
index 81bcba62fe..8c7cf5c0d3 100644
--- a/toolkit/content/tests/chrome/window_chromemargin.xhtml
+++ b/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");
diff --git a/toolkit/content/tests/chrome/window_cursorsnap_dialog.xhtml b/toolkit/content/tests/chrome/window_cursorsnap_dialog.xhtml
index d5c0e2753e..fa239a87af 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_keys.xhtml b/toolkit/content/tests/chrome/window_keys.xhtml
index 77a098ef0b..51f3be0a33 100644
--- a/toolkit/content/tests/chrome/window_keys.xhtml
+++ b/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;
 
diff --git a/toolkit/content/tests/chrome/window_largemenu.xhtml b/toolkit/content/tests/chrome/window_largemenu.xhtml
index d84b045e78..8e6b6718b4 100644
--- a/toolkit/content/tests/chrome/window_largemenu.xhtml
+++ b/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("top"), "", gTests[gTestIndex] + " top is empty after moving");
+  is(popup.getAttribute("left"), null, gTests[gTestIndex] + " left 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("top"), "", gTests[gTestIndex] + " top 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"), null, gTests[gTestIndex] + " top is not set after moving to -1");
 
   popup.hidePopup();
 }
diff --git a/toolkit/content/tests/chrome/window_maximized_persist.xhtml b/toolkit/content/tests/chrome/window_maximized_persist.xhtml
index f7eb695f0f..10f7d36d07 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 83fede7fae..e104dfa652 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 524a95b643..2262ba08e9 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/chrome/window_tooltip.xhtml b/toolkit/content/tests/chrome/window_tooltip.xhtml
index b78075de45..e6ee5c6b42 100644
--- a/toolkit/content/tests/chrome/window_tooltip.xhtml
+++ b/toolkit/content/tests/chrome/window_tooltip.xhtml
@@ -30,6 +30,8 @@ var gOriginalWidth = -1;
 var gOriginalHeight = -1;
 var gButton = null;
 
+const kTooltipOffsetVertical = 10;
+
 function runTest()
 {
   startPopupTests(popupTests);
@@ -112,7 +114,7 @@ var popupTests = [
        Math.round(buttonrect.left + parseFloat(popupstyle.marginLeft) + 6),
        testname + " left position of tooltip");
     is(Math.round(rect.top),
-       Math.round(buttonrect.top + parseFloat(popupstyle.marginTop) + 6),
+       Math.round(buttonrect.top + parseFloat(popupstyle.marginTop) + 6 + kTooltipOffsetVertical),
        testname + " top position of tooltip");
 
     var labelrect = document.getElementById("label").getBoundingClientRect();
@@ -159,7 +161,7 @@ var popupTests = [
        Math.round(buttonrect.left + parseFloat(popupstyle.marginLeft) + 4),
        testname + " left position of tooltip");
     is(Math.round(rect.top),
-       Math.round(buttonrect.top + parseFloat(popupstyle.marginTop) + 4),
+       Math.round(buttonrect.top + parseFloat(popupstyle.marginTop) + 4 + kTooltipOffsetVertical),
        testname + " top position of tooltip");
 
     var labelrect = document.getElementById("label").getBoundingClientRect();
@@ -204,7 +206,7 @@ var popupTests = [
        Math.round(buttonrect.left + parseFloat(popupstyle.marginLeft) + 6),
        testname + " left position of tooltip");
     is(Math.round(rect.top),
-       Math.round(buttonrect.top + parseFloat(popupstyle.marginTop) + 6),
+       Math.round(buttonrect.top + parseFloat(popupstyle.marginTop) + 6 + kTooltipOffsetVertical),
        testname + " top position of tooltip");
 
     var labelrect = document.getElementById("label").getBoundingClientRect();
@@ -327,7 +329,43 @@ var popupTests = [
     // that the original height has increased by at least 10 pixels
     ok(gOriginalHeight + 10 < rect.bottom - rect.top, testname + " tooltip is wrapped");
   }
-}
+},
+{
+  testname: "anchored tooltip with no offset",
+  events: ["popupshowing thetooltip", "popupshown thetooltip"],
+  autohide: "thetooltip",
+  test() {
+    gButton = document.getElementById("withtooltip");
+    document
+      .getElementById("thetooltip")
+      .setAttribute(
+        "onpopupshowing",
+        "this.moveToAnchor(this.triggerNode, 'after_start');"
+      );
+    disableNonTestMouse(true);
+    synthesizeMouse(gButton, 2, 2, { type: "mouseover" });
+    synthesizeMouse(gButton, 4, 4, { type: "mousemove" });
+    synthesizeMouse(gButton, 6, 6, { type: "mousemove" });
+    disableNonTestMouse(false);
+  },
+  result(testname) {
+    var buttonrect = document
+      .getElementById("withtooltip")
+      .getBoundingClientRect();
+    var tooltip = document.getElementById("thetooltip");
+    var rect = tooltip.getBoundingClientRect();
+    var popupstyle = window.getComputedStyle(tooltip);
+
+    // Offset does not apply to anchored tooltips
+    is(
+      Math.round(rect.top),
+      Math.round(buttonrect.bottom + parseFloat(popupstyle.marginTop)),
+      testname + " top position of tooltip"
+    );
+
+    tooltip.removeAttribute("onpopupshowing");
+  },
+},
 ];
 
 var waitSteps = 0;
@@ -359,7 +397,14 @@ function moveWindowTo(x, y, callback, arg)
   }
 }
 
-window.arguments[0].SimpleTest.waitForFocus(runTest, window);
+(async function() {
+  let parent = window.arguments[0];
+  await Promise.all([
+    parent.SimpleTest.promiseFocus(window),
+    parent.SpecialPowers.pushPrefEnv({set: [["ui.tooltipOffsetVertical", kTooltipOffsetVertical]]}),
+  ]);
+  runTest();
+})();
 ]]>
 </script>
 
diff --git a/toolkit/content/tests/widgets/chrome.toml b/toolkit/content/tests/widgets/chrome.toml
index 18fe0d153a..fa10249e89 100644
--- a/toolkit/content/tests/widgets/chrome.toml
+++ b/toolkit/content/tests/widgets/chrome.toml
@@ -5,7 +5,7 @@ support-files = [
   "popup_shared.js",
   "window_label_checkbox.xhtml",
   "window_menubar.xhtml",
-  "seek_with_sound.ogg",
+  "seek_with_sound.webm",
 ]
 prefs = ["app.support.baseURL='https://support.mozilla.org/'"]
 
@@ -63,7 +63,7 @@ skip-if = [
 ["test_videocontrols_focus.html"]
 support-files = [
   "head.js",
-  "video.ogg",
+  "video.webm",
 ]
 skip-if = [
   "os == 'android'",
diff --git a/toolkit/content/tests/widgets/file_videocontrols_jsdisabled.html b/toolkit/content/tests/widgets/file_videocontrols_jsdisabled.html
index 56917b69ac..95dba91eea 100644
--- a/toolkit/content/tests/widgets/file_videocontrols_jsdisabled.html
+++ b/toolkit/content/tests/widgets/file_videocontrols_jsdisabled.html
@@ -1,2 +1,2 @@
-<video src="seek_with_sound.ogg" controls autoplay=true></video>
+<video src="seek_with_sound.webm" controls autoplay=true></video>
 <script>window.testExpando = true;</script>
diff --git a/toolkit/content/tests/widgets/head.js b/toolkit/content/tests/widgets/head.js
index d7473fa92d..2a72845a27 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/mochitest.toml b/toolkit/content/tests/widgets/mochitest.toml
index 7e20352256..efd86f1208 100644
--- a/toolkit/content/tests/widgets/mochitest.toml
+++ b/toolkit/content/tests/widgets/mochitest.toml
@@ -5,8 +5,8 @@ support-files = [
   "file_videocontrols_jsdisabled.html",
   "image.png",
   "image-zh.png",
-  "seek_with_sound.ogg",
-  "video.ogg",
+  "seek_with_sound.webm",
+  "video.webm",
   "head.js",
   "tree_shared.js",
   "test-webvtt-1.vtt",
@@ -97,7 +97,10 @@ skip-if = [
 ["test_videocontrols_size.html"]
 
 ["test_videocontrols_standalone.html"]
-skip-if = ["os == 'android'"] # bug 1075573
+skip-if = [
+  "os == 'linux'", # bug 1804621
+  "os == 'android'", # bug 1075573
+]
 
 ["test_videocontrols_video_direction.html"]
 skip-if = [
diff --git a/toolkit/content/tests/widgets/seek_with_sound.ogg b/toolkit/content/tests/widgets/seek_with_sound.ogg
deleted file mode 100644
index c86d9946bd..0000000000
--- a/toolkit/content/tests/widgets/seek_with_sound.ogg
+++ /dev/null
diff --git a/toolkit/content/tests/widgets/seek_with_sound.webm b/toolkit/content/tests/widgets/seek_with_sound.webm
new file mode 100644
index 0000000000..dd60cc5a0a
--- /dev/null
+++ b/toolkit/content/tests/widgets/seek_with_sound.webm
diff --git a/toolkit/content/tests/widgets/test_moz_button.html b/toolkit/content/tests/widgets/test_moz_button.html
index 473b2d1a1c..a849ccc956 100644
--- a/toolkit/content/tests/widgets/test_moz_button.html
+++ b/toolkit/content/tests/widgets/test_moz_button.html
@@ -75,24 +75,23 @@
         color: "--button-text-color-primary",
         height: "--button-min-height",
       });
-
       assertButtonPropertiesMatch(four, {
         width: "--button-size-icon",
         height: "--button-size-icon",
         backgroundColor: "--button-background-color",
-        fill: "--button-text-color",
+        fill: "--icon-color",
       });
       assertButtonPropertiesMatch(five, {
         width: "--button-size-icon",
         height: "--button-size-icon",
         backgroundColor: "transparent",
-        fill: "--button-text-color",
+        fill: "--icon-color",
       });
       assertButtonPropertiesMatch(six, {
         width: "--button-size-icon",
         height: "--button-size-icon",
         backgroundColor: "transparent",
-        fill: "--button-text-color",
+        fill: "--icon-color",
       });
 
       buttons.forEach(btn => (btn.size = "small"));
diff --git a/toolkit/content/tests/widgets/test_moz_card.html b/toolkit/content/tests/widgets/test_moz_card.html
index ef4e67d0fa..aa9ecfde31 100644
--- a/toolkit/content/tests/widgets/test_moz_card.html
+++ b/toolkit/content/tests/widgets/test_moz_card.html
@@ -13,6 +13,11 @@
 
 <body>
   <p id="display"></p>
+  <style>
+    moz-card.withHeadingIcon::part(icon) {
+      background-image: url("chrome://browser/skin/preferences/category-general.svg");
+    }
+  </style>
   <div id="content">
     <moz-card id="default-card" data-l10n-id="test-id-1" data-l10n-attrs="heading">
       <div>TEST</div>
@@ -25,6 +30,12 @@
     </moz-card>
     <hr />
 
+    <moz-card id="heading-icon-card" data-l10n-id="test-id-3" data-l10n-attrs="heading" heading="heading with icon"
+      type="accordion" icon class="withHeadingIcon">
+      <div>heading icon test content</div>
+    </moz-card>
+    <hr />
+
   </div>
   <pre id="test"></pre>
   <script>
@@ -58,12 +69,16 @@
 
     }
 
-    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");
     }
 
+    function assertHeadingIconCardProperties(card) {
+      ok(card.shadowRoot.querySelector("#heading-wrapper").querySelector("#heading-icon"), "The heading icon element should exist");
+    }
+
     async function generateCard(values) {
       let card = document.createElement("moz-card");
       for (let [key, value] of Object.entries(values)) {
@@ -152,6 +167,54 @@
       );
     });
 
+    add_task(async function testHeadingIconCard() {
+      assertBasicProperties(document.getElementById("heading-icon-card"),
+        {
+          "data-l10n-id": "test-id-3",
+          "data-l10n-attrs": "heading",
+          contentText: "heading icon test content",
+          headingText: "heading with icon",
+        }
+      );
+      assertHeadingIconCardProperties(document.getElementById("heading-icon-card"),
+        {
+          "data-l10n-id": "test-id-3",
+          "data-l10n-attrs": "heading",
+          contentText: "heading icon test content",
+          headingText: "heading with icon",
+        }
+      );
+
+      let headingIconCard = await generateCard(
+        {
+          class: "heading-icon-class",
+          type: "accordion",
+          icon: "",
+          id: "generated-heading-icon-card",
+          "data-l10n-id": "generated-id-3",
+          "data-l10n-attrs": "heading",
+          heading: testHeading
+        }
+      );
+
+      assertBasicProperties(headingIconCard,
+        {
+          "data-l10n-id": "generated-id-3",
+          "data-l10n-attrs": "heading",
+          headingText: testHeading,
+          contentText: generatedSlotText,
+        }
+      );
+      assertHeadingIconCardProperties(headingIconCard,
+        {
+          "data-l10n-id": "generated-id-3",
+          "data-l10n-attrs": "heading",
+          headingText: testHeading,
+          contentText: generatedSlotText,
+        }
+      );
+    });
+
   </script>
 </body>
 
diff --git a/toolkit/content/tests/widgets/test_popupreflows.xhtml b/toolkit/content/tests/widgets/test_popupreflows.xhtml
index c3f8068779..c014d6bee4 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 076b4350fd..f2fc53a1cc 100644
--- a/toolkit/content/tests/widgets/test_videocontrols.html
+++ b/toolkit/content/tests/widgets/test_videocontrols.html
@@ -184,7 +184,7 @@ add_task(async function setup() {
       ]});
   await new Promise(resolve => {
     video.addEventListener("canplaythrough", resolve, {once: true});
-    video.src = "seek_with_sound.ogg";
+    video.src = "seek_with_sound.webm";
   });
 
   video.addEventListener("play", captureEventThenCheck);
@@ -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 ad528f4c27..0a7a2dcbc3 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_closed_caption_menu.html b/toolkit/content/tests/widgets/test_videocontrols_closed_caption_menu.html
index 39d6ff494f..5a2602d204 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_closed_caption_menu.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_closed_caption_menu.html
@@ -49,7 +49,7 @@
       ["media.videocontrols.keyboard-tab-to-all-controls", true],
     ]}, done);
   }, done => {
-    video.src = "seek_with_sound.ogg";
+    video.src = "seek_with_sound.webm";
     video.addEventListener("loadedmetadata", done);
   }, cleanup);
 
diff --git a/toolkit/content/tests/widgets/test_videocontrols_error.html b/toolkit/content/tests/widgets/test_videocontrols_error.html
index af90a4672a..922726d5be 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_error.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_error.html
@@ -27,7 +27,7 @@
 
   add_task(async function check_normal_status() {
     await new Promise(resolve => {
-      video.src = "seek_with_sound.ogg";
+      video.src = "seek_with_sound.webm";
       video.addEventListener("loadedmetadata", () => SimpleTest.executeSoon(resolve));
     });
 
@@ -44,7 +44,7 @@
     const errorType = "errorNoSource";
 
     await new Promise(resolve => {
-      video.src = "invalid_source.ogg";
+      video.src = "invalid_source.webm";
       video.addEventListener("error", () => SimpleTest.executeSoon(resolve));
     });
 
diff --git a/toolkit/content/tests/widgets/test_videocontrols_focus.html b/toolkit/content/tests/widgets/test_videocontrols_focus.html
index 0982947ffe..e19262bf6e 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_focus.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_focus.html
@@ -36,7 +36,7 @@ add_task(async function setup() {
   video.controls = true;
   video.preload = "auto";
   video.loop = true;
-  video.src = "video.ogg";
+  video.src = "video.webm";
   const caption = video.addTextTrack("captions", "English", "en");
   caption.mode = "showing";
   const content = document.getElementById("content");
diff --git a/toolkit/content/tests/widgets/test_videocontrols_iframe_fullscreen.html b/toolkit/content/tests/widgets/test_videocontrols_iframe_fullscreen.html
index 0a74b25609..d30d10b8bc 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_iframe_fullscreen.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_iframe_fullscreen.html
@@ -30,7 +30,7 @@
       ifr.addEventListener("load", resolve);
     }).then(() => new Promise(resolve => {
       video = ifr.contentDocument.getElementById("video");
-      video.src = "seek_with_sound.ogg";
+      video.src = "seek_with_sound.webm";
       video.addEventListener("loadedmetadata", resolve);
     })).then(() => new Promise(resolve => {
       const available = video.ownerDocument.fullscreenEnabled;
diff --git a/toolkit/content/tests/widgets/test_videocontrols_jsdisabled.html b/toolkit/content/tests/widgets/test_videocontrols_jsdisabled.html
index f3fdecc47f..16cf2b92e0 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_keyhandler.html b/toolkit/content/tests/widgets/test_videocontrols_keyhandler.html
index 5b771fc745..9737a9fff2 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_keyhandler.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_keyhandler.html
@@ -31,7 +31,7 @@
       ["media.videocontrols.keyboard-tab-to-all-controls", true],
     ]}, done);
   }, done => {
-    video.src = "seek_with_sound.ogg";
+    video.src = "seek_with_sound.webm";
     video.addEventListener("loadedmetadata", done);
   });
 
diff --git a/toolkit/content/tests/widgets/test_videocontrols_onclickplay.html b/toolkit/content/tests/widgets/test_videocontrols_onclickplay.html
index 9023512ab7..3b1bd4653c 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_onclickplay.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_onclickplay.html
@@ -22,11 +22,11 @@ var video = document.getElementById("video");
 
 function startMediaLoad() {
   // Kick off test once video has loaded, in its canplaythrough event handler.
-  video.src = "seek_with_sound.ogg";
+  video.src = "seek_with_sound.webm";
   video.addEventListener("canplaythrough", runTest);
 }
 
-function loadevent(event) {
+function loadevent() {
   SpecialPowers.pushPrefEnv({"set": [["media.cache_size", 40000]]}, startMediaLoad);
 }
 
diff --git a/toolkit/content/tests/widgets/test_videocontrols_scrubber_position.html b/toolkit/content/tests/widgets/test_videocontrols_scrubber_position.html
index b1d2ab9e74..51117e7955 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_scrubber_position.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_scrubber_position.html
@@ -26,7 +26,7 @@ const video = document.getElementById("video");
 add_task(async function setup() {
   await new Promise(resolve => {
     video.addEventListener("canplaythrough", resolve, {once: true});
-    video.src = "seek_with_sound.ogg";
+    video.src = "seek_with_sound.webm";
   });
 
   // Check initial state upon load
diff --git a/toolkit/content/tests/widgets/test_videocontrols_scrubber_position_nopreload.html b/toolkit/content/tests/widgets/test_videocontrols_scrubber_position_nopreload.html
index 9fbb6fbcb5..968ba5db96 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_scrubber_position_nopreload.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_scrubber_position_nopreload.html
@@ -13,7 +13,7 @@
 <p id="display"></p>
 
 <div id="content">
-  <video width="320" height="240" id="video" mozNoDynamicControls controls="true" preload="none" src="seek_with_sound.ogg"></video>
+  <video width="320" height="240" id="video" mozNoDynamicControls controls="true" preload="none" src="seek_with_sound.webm"></video>
 </div>
 
 <div id="host"></div>
diff --git a/toolkit/content/tests/widgets/test_videocontrols_size.html b/toolkit/content/tests/widgets/test_videocontrols_size.html
index 559cc66e86..d940b1d295 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_size.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_size.html
@@ -148,7 +148,7 @@
 
   testCases.push(() => Promise.all(videoElems.map(video => new Promise(resolve => {
     video.addEventListener("loadedmetadata", resolve);
-    video.src = "seek_with_sound.ogg";
+    video.src = "seek_with_sound.webm";
   }))));
 
   videoElems.forEach(video => {
diff --git a/toolkit/content/tests/widgets/test_videocontrols_standalone.html b/toolkit/content/tests/widgets/test_videocontrols_standalone.html
index 14208923dd..1eaa026cdc 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_standalone.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_standalone.html
@@ -22,7 +22,7 @@ function getMediaElement(aWindow) {
   return aWindow.document.getElementsByTagName("video")[0];
 }
 
-var popup = window.open("seek_with_sound.ogg");
+var popup = window.open("seek_with_sound.webm");
 popup.addEventListener("load", function() {
   var video = getMediaElement(popup);
 
diff --git a/toolkit/content/tests/widgets/test_videocontrols_video_noaudio.html b/toolkit/content/tests/widgets/test_videocontrols_video_noaudio.html
index bfc8018466..99d5bdad01 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_video_noaudio.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_video_noaudio.html
@@ -23,7 +23,7 @@
   add_task(async function setup() {
     await SpecialPowers.pushPrefEnv({"set": [["media.cache_size", 40000]]});
     await new Promise(resolve => {
-      video.src = "video.ogg";
+      video.src = "video.webm";
       video.addEventListener("loadedmetadata", () => SimpleTest.executeSoon(resolve));
     });
   });
diff --git a/toolkit/content/tests/widgets/test_videocontrols_vtt.html b/toolkit/content/tests/widgets/test_videocontrols_vtt.html
index 2f8d70f35a..33b8bcf24e 100644
--- a/toolkit/content/tests/widgets/test_videocontrols_vtt.html
+++ b/toolkit/content/tests/widgets/test_videocontrols_vtt.html
@@ -26,7 +26,7 @@
   add_task(async function wait_for_media_ready() {
     await SpecialPowers.pushPrefEnv({"set": [["media.cache_size", 40000]]});
     await new Promise(resolve => {
-      video.src = "seek_with_sound.ogg";
+      video.src = "seek_with_sound.webm";
       video.addEventListener("loadedmetadata", resolve);
     });
   });
diff --git a/toolkit/content/tests/widgets/tree_shared.js b/toolkit/content/tests/widgets/tree_shared.js
index ba52bf828e..2cc40686ec 100644
--- a/toolkit/content/tests/widgets/tree_shared.js
+++ b/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(
-      properties,
-      expectedProperties ? expectedProperties : "",
-      adjtestid + "getColumnProperties"
-    );
+    is(properties, expectedProperties || "", adjtestid + "getColumnProperties");
   }
 
   is(columns.getFirstColumn(), columns[0], testid + "getFirstColumn");
@@ -574,10 +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++;
   }
 
@@ -1307,7 +1303,7 @@ function testtag_tree_TreeView_rows(tree, testid, rowInfo, startRow) {
     isContainer(row) {
       return row.container;
     },
-    isContainerOpen(row) {
+    isContainerOpen() {
       return false;
     },
     isContainerEmpty(row) {
@@ -1325,7 +1321,7 @@ function testtag_tree_TreeView_rows(tree, testid, rowInfo, startRow) {
     getParentIndex(row) {
       return row.parent;
     },
-    hasNextSibling(row) {
+    hasNextSibling() {
       return r < startRow + length - 1;
     },
   };
@@ -1433,7 +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;
@@ -1734,7 +1730,7 @@ function testtag_tree_wheel(aTree) {
 
   var defaultPrevented = 0;
 
-  function wheelListener(event) {
+  function wheelListener() {
     defaultPrevented++;
   }
   window.addEventListener("wheel", wheelListener);
@@ -2109,7 +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);
@@ -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"),
-          value: cell.getAttribute("value"),
-          properties: cell.getAttribute("properties"),
+          label: cell.getAttribute("label") || "",
+          value: cell.getAttribute("value") || "",
+          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,
diff --git a/toolkit/content/tests/widgets/video.ogg b/toolkit/content/tests/widgets/video.ogg
deleted file mode 100644
index ac7ece3519..0000000000
--- a/toolkit/content/tests/widgets/video.ogg
+++ /dev/null
diff --git a/toolkit/content/tests/widgets/video.webm b/toolkit/content/tests/widgets/video.webm
new file mode 100644
index 0000000000..87a8d837a8
--- /dev/null
+++ b/toolkit/content/tests/widgets/video.webm
diff --git a/toolkit/content/tests/widgets/videocontrols_direction_test.js b/toolkit/content/tests/widgets/videocontrols_direction_test.js
index e937f06b3f..608a39cc5b 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 c4ced844ad..ded1361365 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