--- a/browser/components/extensions/test/browser/browser_ext_find.js
+++ b/browser/components/extensions/test/browser/browser_ext_find.js
@@ -1,35 +1,32 @@
 /* global browser */
 "use strict";
 
 function frameScript() {
-  function getSelectedText() {
-    let frame = this.content.frames[0].frames[1];
-    let docShell = frame.docShell;
-    let controller = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
-                             .getInterface(Ci.nsISelectionDisplay)
-                             .QueryInterface(Ci.nsISelectionController);
-    let selection = controller.getSelection(controller.SELECTION_FIND);
-    let range = selection.getRangeAt(0);
-    let scope = {};
-    ChromeUtils.import("resource://gre/modules/FindContent.jsm", scope);
-    let highlighter = (new scope.FindContent(docShell)).highlighter;
-    let r1 = frame.parent.frameElement.getBoundingClientRect();
-    let f1 = highlighter._getFrameElementOffsets(frame.parent);
-    let r2 = frame.frameElement.getBoundingClientRect();
-    let f2 = highlighter._getFrameElementOffsets(frame);
-    let r3 = range.getBoundingClientRect();
-    let rect = {
-      top: (r1.top + r2.top + r3.top + f1.y + f2.y),
-      left: (r1.left + r2.left + r3.left + f1.x + f2.x),
-    };
-    this.sendAsyncMessage("test:find:selectionTest", {text: selection.toString(), rect});
-  }
-  getSelectedText();
+  let frame = this.content.frames[0].frames[1];
+  let docShell = frame.docShell;
+  let controller = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
+                           .getInterface(Ci.nsISelectionDisplay)
+                           .QueryInterface(Ci.nsISelectionController);
+  let selection = controller.getSelection(controller.SELECTION_FIND);
+  let range = selection.getRangeAt(0);
+  let scope = {};
+  ChromeUtils.import("resource://gre/modules/FindContent.jsm", scope);
+  let highlighter = (new scope.FindContent(docShell)).highlighter;
+  let r1 = frame.parent.frameElement.getBoundingClientRect();
+  let f1 = highlighter._getFrameElementOffsets(frame.parent);
+  let r2 = frame.frameElement.getBoundingClientRect();
+  let f2 = highlighter._getFrameElementOffsets(frame);
+  let r3 = range.getBoundingClientRect();
+  let rect = {
+    top: (r1.top + r2.top + r3.top + f1.y + f2.y),
+    left: (r1.left + r2.left + r3.left + f1.x + f2.x),
+  };
+  this.sendAsyncMessage("test:find:selectionTest", {text: selection.toString(), rect});
 }
 
 function waitForMessage(messageManager, topic) {
   return new Promise(resolve => {
     messageManager.addMessageListener(topic, function messageListener(message) {
       messageManager.removeMessageListener(topic, messageListener);
       resolve(message);
     });
@@ -139,17 +136,17 @@ add_task(async function testDuplicatePin
 
   await extension.startup();
   let rectData = await extension.awaitMessage("test:find:WebExtensionFinished");
   let {top, left} = rectData[5].rectsAndTexts.rectList[0];
   await extension.unload();
 
   let {selectedBrowser} = gBrowser;
 
-  let frameScriptUrl = `data:,(${frameScript})()`;
+  let frameScriptUrl = `data:,(${frameScript}).call(this)`;
   selectedBrowser.messageManager.loadFrameScript(frameScriptUrl, false);
   let message = await waitForMessage(selectedBrowser.messageManager, "test:find:selectionTest");
 
   info("Test that text was highlighted properly.");
   is(message.data.text, "bananA", `The text that was highlighted: - Expected: bananA, Actual: ${message.data.text}`);
 
   info("Test that rectangle data returned from the search matches the highlighted result.");
   is(message.data.rect.top, top, `rect.top: - Expected: ${message.data.rect.top}, Actual: ${top}`);

--- a/browser/components/extensions/test/browser/browser_ext_webNavigation_onCreatedNavigationTarget.js
+++ b/browser/components/extensions/test/browser/browser_ext_webNavigation_onCreatedNavigationTarget.js
@@ -114,17 +114,17 @@ add_task(async function test_on_created_
 
   const expectedSourceTab = await extension.awaitMessage("expectedSourceTab");
 
   info("Open a subframe link in a new tab using Ctrl-click");
 
   await runCreatedNavigationTargetTest({
     extension,
     openNavTarget() {
-      BrowserTestUtils.synthesizeMouseAtCenter(function() {
+      BrowserTestUtils.synthesizeMouseAtCenter(() => {
         // This code runs as a framescript in the child process and it returns the
         // target link in the subframe.
         return this.content.frames[0].document
           .querySelector("#test-create-new-tab-from-mouse-click-subframe");
       }, {ctrlKey: true, metaKey: true}, tab.linkedBrowser);
     },
     expectedWebNavProps: {
       sourceTabId: expectedSourceTab.sourceTabId,
@@ -133,17 +133,17 @@ add_task(async function test_on_created_
     },
   });
 
   info("Open a subframe link in a new window using Shift-click");
 
   await runCreatedNavigationTargetTest({
     extension,
     openNavTarget() {
-      BrowserTestUtils.synthesizeMouseAtCenter(function() {
+      BrowserTestUtils.synthesizeMouseAtCenter(() => {
         // This code runs as a framescript in the child process and it returns the
         // target link in the subframe.
         return this.content.frames[0].document
                       .querySelector("#test-create-new-window-from-mouse-click-subframe");
       }, {shiftKey: true}, tab.linkedBrowser);
     },
     expectedWebNavProps: {
       sourceTabId: expectedSourceTab.sourceTabId,
@@ -152,17 +152,17 @@ add_task(async function test_on_created_
     },
   });
 
   info("Open a subframe link with target=\"_blank\" in a new tab using click");
 
   await runCreatedNavigationTargetTest({
     extension,
     openNavTarget() {
-      BrowserTestUtils.synthesizeMouseAtCenter(function() {
+      BrowserTestUtils.synthesizeMouseAtCenter(() => {
         // This code runs as a framescript in the child process and it returns the
         // target link in the subframe.
         return this.content.frames[0].document
           .querySelector("#test-create-new-tab-from-targetblank-click-subframe");
       }, {}, tab.linkedBrowser);
     },
     expectedWebNavProps: {
       sourceTabId: expectedSourceTab.sourceTabId,

--- a/browser/components/extensions/test/browser/browser_ext_webNavigation_onCreatedNavigationTarget_contextmenu.js
+++ b/browser/components/extensions/test/browser/browser_ext_webNavigation_onCreatedNavigationTarget_contextmenu.js
@@ -109,17 +109,17 @@ add_task(async function test_on_created_
   const expectedSourceTab = await extension.awaitMessage("expectedSourceTab");
 
   info("Open a subframe link in a new tab from the context menu");
 
   await runCreatedNavigationTargetTest({
     extension,
     async openNavTarget() {
       await clickContextMenuItem({
-        pageElementSelector: function() {
+        pageElementSelector: () => {
           // This code runs as a framescript in the child process and it returns the
           // target link in the subframe.
           return this.content.frames[0]
             .document.querySelector("#test-create-new-tab-from-context-menu-subframe");
         },
         contextMenuItemLabel: "Open Link in New Tab",
       });
     },
@@ -131,17 +131,17 @@ add_task(async function test_on_created_
   });
 
   info("Open a subframe link in a new window from the context menu");
 
   await runCreatedNavigationTargetTest({
     extension,
     async openNavTarget() {
       await clickContextMenuItem({
-        pageElementSelector: function() {
+        pageElementSelector: () => {
           // This code runs as a framescript in the child process and it returns the
           // target link in the subframe.
           return this.content.frames[0]
             .document.querySelector("#test-create-new-window-from-context-menu-subframe");
         },
         contextMenuItemLabel: "Open Link in New Window",
       });
     },

--- a/dom/base/test/browser_messagemanager_loadprocessscript.js
+++ b/dom/base/test/browser_messagemanager_loadprocessscript.js
@@ -33,17 +33,17 @@ function processScript() {
   this.cpmm = Services.cpmm;
 
   addMessageListener("ProcessTest:Reply", function listener(msg) {
     removeMessageListener("ProcessTest:Reply", listener);
     sendAsyncMessage("ProcessTest:Finished");
   });
   sendSyncMessage("ProcessTest:Loaded");
 }
-var processScriptURL = "data:,(" + processScript.toString() + ")()";
+var processScriptURL = "data:,(" + processScript.toString() + ").call(this)";
 
 function initTestScript() {
   let init = initialProcessData;
   if (init.test123 != "hello") {
     dump("Initial data incorrect\n");
     return;
   }
 

--- a/toolkit/components/extensions/test/xpcshell/test_ext_permissions.js
+++ b/toolkit/components/extensions/test/xpcshell/test_ext_permissions.js
@@ -31,17 +31,17 @@ function frameScript() {
     },
   });
 }
 
 async function withHandlingUserInput(extension, fn) {
   let {messageManager} = extension.extension.groupFrameLoader;
 
   if (!extensionHandlers.has(extension)) {
-    messageManager.loadFrameScript(`data:,(${frameScript})(this)`, false);
+    messageManager.loadFrameScript(`data:,(${frameScript}).call(this)`, false);
     extensionHandlers.add(extension);
   }
 
   await MessageChannel.sendMessage(messageManager, "ExtensionTest:HandleUserInput", true);
   await fn();
   await MessageChannel.sendMessage(messageManager, "ExtensionTest:HandleUserInput", false);
 }