--- a/mobile/android/components/extensions/test/mochitest/test_ext_pageAction.html
+++ b/mobile/android/components/extensions/test/mochitest/test_ext_pageAction.html
@@ -13,17 +13,17 @@
 <script type="text/javascript">
 "use strict";
 
 let dataURI = "iVBORw0KGgoAAAANSUhEUgAAACQAAAAkCAYAAADhAJiYAAAC4klEQVRYhdWXLWzbQBSADQtDAwsHC1tUhUxqfL67lk2tdn+OJg0ODU0rLByqgqINBY6tmlbn7LMTJ5FaFVVBk1G0oUGjG2jT2Y7jxmmcbU/6iJ+f36fz+e5sGP9riCGm9hB37RG+scd4Yo/wsDXCZyIE2xuXsce4bY+wXkAsQtzYmExrfFgvkJkRbkzo1ehoxx5iXcgI/9iYUGt8WH9MqDXEcmNChmEYrRCf2SHWeYgQx3x0tLNRIeKQLTtEFyJEep4NTuhk8BC+yMrwEE3+iozo42d8gK7FAOkMsRiiN8QhW2ttSK5QTfRRV4QoymVeJMvPvDp7gCZigD613MN6yRFA3SWarow9QB9LCfG+NeF9qCtjAKOSQjCqVKhfVsiHEQ+grgx/lRGqUihAc1uL8EFD+KCRO+GrF4J61phcoRoPoEzkYhZYpykh5sMb7kOdIeY+jHKur4QI4Feh4AFX1nVeLxrAvQchGsBz5ls6wa2QdwcvIcE2863bTH79KOvsz/uUYJsp+J0pSzNlDckVqqVGUAF+n6uS7txcOl6wot4JVy70ufDLy4pWLUQVPE81pRI0mGe9oxLMHSeohHvMs/STUNaUK6vDPCvOyxMFDx4achehRDJmHnydnkPww5OFfLxrGIZBFDyYl4LpMzlTQFIP6AQx86w2UeYBccFpJrcKv5L9eGDtUAU6RIELqsB74uynjy/UBRF1gS5BTFxwQT1wTiXoUg9MH7m/3NZRRoi5IJytUbMgzv4Wc832+oQkiKgEehmyMkkpKsFkQV11QsRJL5rJYBLItQgRaUZEmnoZXsomz3vGiWw+I9KMF9SVFOqZEemZekli1jN3U/UOqhHHvC6oWWGElhfSpGdOk6+O9prdwvtLj5BjRsQxdRnot+Zeifpy/2/0stktKTRNLmbk0mwXyl8253fyojj+8rxOHNAhjjm5n0/5OOCGOKBzkrMO0Z75lvSAzKlrF32Z/3z8BqLAn+yMV7VhAAAAAElFTkSuQmCC";
 
 let image = atob(dataURI);
 const IMAGE_ARRAYBUFFER = Uint8Array.from(image, byte => byte.charCodeAt(0)).buffer;
 
-function backgroundScript() {
+function background() {
   browser.test.assertTrue("pageAction" in browser, "Namespace 'pageAction' exists in browser");
   browser.test.assertTrue("show" in browser.pageAction, "API method 'show' exists in browser.pageAction");
 
   // TODO: Use the Tabs API to obtain the tab ids for showing pageActions.
   let tabId = 1;
   browser.test.onMessage.addListener(msg => {
     if (msg === "pageAction-show") {
       browser.pageAction.show(tabId).then(() => {
@@ -41,17 +41,17 @@ function backgroundScript() {
     browser.test.sendMessage("page-action-clicked");
   });
 
   browser.test.sendMessage("ready");
 }
 
 add_task(function* test_contentscript() {
   let extension = ExtensionTestUtils.loadExtension({
-    background: "(" + backgroundScript.toString() + ")()",
+    background,
     manifest: {
       "name": "PageAction Extension",
       "page_action": {
         "default_title": "Page Action",
         "default_icon": {
           "18": "extension.png",
         },
       },

--- a/mobile/android/components/extensions/test/mochitest/test_ext_pageAction_popup.html
+++ b/mobile/android/components/extensions/test/mochitest/test_ext_pageAction_popup.html
@@ -16,17 +16,17 @@
 Cu.import("resource://gre/modules/Services.jsm");
 
 let dataURI = "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";
 
 let image = atob(dataURI);
 const IMAGE_ARRAYBUFFER = Uint8Array.from(image, byte => byte.charCodeAt(0)).buffer;
 
 add_task(function* test_contentscript() {
-  function backgroundScript() {
+  function background() {
     // TODO: Use the Tabs API to obtain the tab ids for showing pageActions.
     let tabId = 1;
     let onClickedListenerEnabled = false;
 
     browser.test.onMessage.addListener((msg, details) => {
       if (msg === "page-action-show") {
         // TODO: switch to using .show(tabId).then(...) once bug 1270742 lands.
         browser.pageAction.show(tabId).then(() => {
@@ -66,33 +66,33 @@ add_task(function* test_contentscript() 
         if (details.location == location.href) {
           window.close();
         }
       }
     });
   }
 
   let extension = ExtensionTestUtils.loadExtension({
-    background: `(${backgroundScript}())`,
+    background,
     manifest: {
       "name": "PageAction Extension",
       "page_action": {
         "default_title": "Page Action",
         "default_popup": "default.html",
         "default_icon": {
           "18": "extension.png",
         },
       },
     },
     files: {
-      "default.html": `<html><head><meta charset="utf-8"><script src="popup.js"></${"script"}></head></html>`,
+      "default.html": `<html><head><meta charset="utf-8"><script src="popup.js"><\/script></head></html>`,
       "extension.png": IMAGE_ARRAYBUFFER,
-      "a.html": `<html><head><meta charset="utf-8"><script src="popup.js"></${"script"}></head></html>`,
-      "b.html": `<html><head><meta charset="utf-8"><script src="popup.js"></${"script"}></head></html>`,
-      "popup.js": `(${popupScript})()`,
+      "a.html": `<html><head><meta charset="utf-8"><script src="popup.js"><\/script></head></html>`,
+      "b.html": `<html><head><meta charset="utf-8"><script src="popup.js"><\/script></head></html>`,
+      "popup.js": popupScript,
     },
   });
 
   let tabClosedPromise = () => {
     return new Promise(resolve => {
       let chromeWin = Services.wm.getMostRecentWindow("navigator:browser");
       let BrowserApp = chromeWin.BrowserApp;
 

--- a/toolkit/components/extensions/test/mochitest/test_chrome_ext_background_debug_global.html
+++ b/toolkit/components/extensions/test/mochitest/test_chrome_ext_background_debug_global.html
@@ -24,29 +24,28 @@ const {
 /**
  * This test is asserting that ext-backgroundPage.js successfully sets its
  * debug global in the AddonWrapper provided by XPIProvider.jsm
  *
  * It does _not_ test any functionality in devtools and does not guarantee
  * debugging is actually working correctly end-to-end.
  */
 
-function backgroundScript() {
+function background() {
   window.testThing = "test!";
   browser.test.notifyPass("background script ran");
 }
 
 const ID = "debug@tests.mozilla.org";
 let extensionData = {
   useAddonManager: "temporary",
-  background: "(" + backgroundScript.toString() + ")()",
+  background,
   manifest: {
     applications: {gecko: {id: ID}},
   },
-  files: {},
 };
 
 add_task(function* () {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   yield extension.awaitFinish("background script ran");
 

--- a/toolkit/components/extensions/test/mochitest/test_chrome_ext_background_page.html
+++ b/toolkit/components/extensions/test/mochitest/test_chrome_ext_background_page.html
@@ -21,17 +21,17 @@ Cu.import("resource://testing-common/Tes
 add_task(function* testAlertNotShownInBackgroundWindow() {
   ok(!Services.wm.getEnumerator("alert:alert").hasMoreElements(),
      "Alerts should not be present at the start of the test.");
 
   let consoleOpened = TestUtils.topicObserved("web-console-created");
 
 
   let extension = ExtensionTestUtils.loadExtension({
-    background: "new " + function() {
+    background: function() {
       browser.test.log("background script executed");
 
       alert("I am an alert in the background.");
 
       browser.test.notifyPass("alertCalled");
     },
   });
 

--- a/toolkit/components/extensions/test/mochitest/test_chrome_ext_contentscript_unrecognizedprop_warning.html
+++ b/toolkit/components/extensions/test/mochitest/test_chrome_ext_contentscript_unrecognizedprop_warning.html
@@ -12,17 +12,17 @@
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 const BASE = "http://mochi.test:8888/chrome/toolkit/components/extensions/test/mochitest";
 
 add_task(function* test_contentscript() {
-  function backgroundScript() {
+  function background() {
     browser.runtime.onMessage.addListener((msg) => {
       if (msg == "loaded") {
         browser.tabs.query({active: true, currentWindow: true}).then((tabs) => {
           // NOTE: we're removing the tab from here because doing a win.close()
           // from the chrome test code is raising a "TypeError: can 't access
           // dead object" exception.
           browser.tabs.remove(tabs[0].id);
 
@@ -42,20 +42,20 @@ add_task(function* test_contentscript() 
         {
           "matches": ["http://mochi.test/*/file_sample.html"],
           "js": ["content_script.js"],
           "run_at": "document_idle",
           "unrecognized_property": "with-a-random-value",
         },
       ],
     },
-    background: "(" + backgroundScript.toString() + ")()",
+    background,
 
     files: {
-      "content_script.js": "(" + contentScript.toString() + ")()",
+      "content_script.js": contentScript,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   SimpleTest.waitForExplicitFinish();
   let waitForConsole = new Promise(resolve => {
     SimpleTest.monitorConsole(resolve, [{

--- a/toolkit/components/extensions/test/mochitest/test_chrome_ext_eventpage_warning.html
+++ b/toolkit/components/extensions/test/mochitest/test_chrome_ext_eventpage_warning.html
@@ -20,20 +20,20 @@ function createEventPageExtension(eventP
     browser.test.sendMessage("running", 1);
   }
 
   return ExtensionTestUtils.loadExtension({
     manifest: {
       "background": eventPage,
     },
     files: {
-      "event-page-script.js": `(${eventPageScript})()`,
+      "event-page-script.js": eventPageScript,
       "event-page.html": `<html><head>
         <meta charset="utf-8">
-        <script src="event-page-script.js"></${"script"}>
+        <script src="event-page-script.js"><\/script>
       </head></html>`,
     },
   });
 }
 
 add_task(function* test_eventpages() {
   // Used in other tests to prevent the monitorConsole to grip.
   SimpleTest.waitForExplicitFinish();

--- a/toolkit/components/extensions/test/mochitest/test_chrome_ext_shutdown_cleanup.html
+++ b/toolkit/components/extensions/test/mochitest/test_chrome_ext_shutdown_cleanup.html
@@ -22,17 +22,17 @@ const {GlobalManager} = Cu.import("resou
 
 /* eslint-disable mozilla/balanced-listeners */
 
 add_task(function* testShutdownCleanup() {
   is(GlobalManager.initialized, false,
      "GlobalManager start as not initialized");
 
   let extension = ExtensionTestUtils.loadExtension({
-    background: "new " + function() {
+    background: function() {
       browser.test.notifyPass("background page loaded");
     },
   });
 
   yield extension.startup();
 
   yield extension.awaitFinish("background page loaded");
 

--- a/toolkit/components/extensions/test/mochitest/test_chrome_ext_storage_cleanup.html
+++ b/toolkit/components/extensions/test/mochitest/test_chrome_ext_storage_cleanup.html
@@ -101,17 +101,17 @@ add_task(function* test_uninstall() {
   yield SpecialPowers.pushPrefEnv({
     set: [["extensions.webextensions.keepUuidOnUninstall", true]],
   });
   yield SpecialPowers.pushPrefEnv({
     set: [["extensions.webextensions.keepStorageOnUninstall", true]],
   });
 
   let extension = ExtensionTestUtils.loadExtension({
-    background: `(${writeData})()`,
+    background: writeData,
     manifest: {
       applications: {gecko: {id: ID}},
       permissions: ["storage"],
     },
     useAddonManager: "temporary",
   });
 
   yield extension.startup();
@@ -120,17 +120,17 @@ add_task(function* test_uninstall() {
 
   // Check that we can still see data we wrote to storage but clear the
   // "leave storage" flag so our storaged gets cleared on uninstall.
   // This effectively tests the keepUuidOnUninstall logic, which ensures
   // that when we read storage again and check that it is cleared, that
   // it is actually a meaningful test!
   yield SpecialPowers.popPrefEnv();
   extension = ExtensionTestUtils.loadExtension({
-    background: `(${readData})()`,
+    background: readData,
     manifest: {
       applications: {gecko: {id: ID}},
       permissions: ["storage"],
     },
     useAddonManager: "temporary",
   });
 
   yield extension.startup();
@@ -138,17 +138,17 @@ add_task(function* test_uninstall() {
   is(results.matchLocalStorage, true, "localStorage data is still present");
   is(results.matchIDB, true, "indexedDB data is still present");
   is(results.matchBrowserStorage, true, "browser.storage.local data is still present");
 
   yield extension.unload();
 
   // Read again.  This time, our data should be gone.
   extension = ExtensionTestUtils.loadExtension({
-    background: `(${readData})()`,
+    background: readData,
     manifest: {
       applications: {gecko: {id: ID}},
       permissions: ["storage"],
     },
     useAddonManager: "temporary",
   });
 
   yield extension.startup();

--- a/toolkit/components/extensions/test/mochitest/test_chrome_ext_trustworthy_origin.html
+++ b/toolkit/components/extensions/test/mochitest/test_chrome_ext_trustworthy_origin.html
@@ -20,23 +20,22 @@
 
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyServiceGetter(this, "gContentSecurityManager",
                                    "@mozilla.org/contentsecuritymanager;1",
                                    "nsIContentSecurityManager");
 
 add_task(function* () {
-  function backgroundScript() {
+  function background() {
     browser.test.sendMessage("ready", browser.runtime.getURL("/test.html"));
   }
 
   let extensionData = {
-    background: "(" + backgroundScript.toString() + ")()",
-    manifest: {},
+    background,
     files: {
       "test.html": `<html><head></head><body></body></html>`,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 

--- a/toolkit/components/extensions/test/mochitest/test_chrome_ext_webnavigation_resolved_urls.html
+++ b/toolkit/components/extensions/test/mochitest/test_chrome_ext_webnavigation_resolved_urls.html
@@ -10,17 +10,17 @@
   <link rel="stylesheet" href="chrome://mochikit/contents/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* webnav_unresolved_uri_on_expected_URI_scheme() {
-  function backgroundScript() {
+  function background() {
     let checkURLs;
 
     browser.webNavigation.onCompleted.addListener((msg) => {
       if (checkURLs.length > 0) {
         let expectedURL = checkURLs.shift();
         browser.test.assertEq(expectedURL, msg.url, "Got the expected URL");
         browser.tabs.remove(msg.tabId).then(() => {
           browser.test.sendMessage("next");
@@ -38,17 +38,17 @@ add_task(function* webnav_unresolved_uri
   }
 
   let extensionData = {
     manifest: {
       permissions: [
         "webNavigation",
       ],
     },
-    background: "new " + backgroundScript,
+    background,
     files: {
       "tab.html": `<!DOCTYPE html>
         <html>
           <head>
            <meta charset="utf-8">
           </head>
         </html>
       `,

--- a/toolkit/components/extensions/test/mochitest/test_ext_background_api_injection.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_background_api_injection.html
@@ -10,17 +10,17 @@
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* testBackgroundWindow() {
   let extension = ExtensionTestUtils.loadExtension({
-    background: "new " + function() {
+    background: function() {
       const BASE = "http://mochi.test:8888/tests/toolkit/components/extensions/test/mochitest";
 
       browser.test.log("background script executed");
       window.location = `${BASE}/file_privilege_escalation.html`;
     },
   });
 
   let awaitConsole = new Promise(resolve => {

--- a/toolkit/components/extensions/test/mochitest/test_ext_background_canvas.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_background_canvas.html
@@ -27,17 +27,17 @@ add_task(function* test_background_canva
       browser.test.notifyPass("background-canvas");
     } catch (e) {
       browser.test.fail(`Error: ${e} :: ${e.stack}`);
       browser.test.notifyFail("background-canvas");
     }
   }
 
   let extensionData = {
-    background: `(${background})()`,
+    background,
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   yield extension.startup();
   yield extension.awaitFinish("background-canvas");
   yield extension.unload();
 });

--- a/toolkit/components/extensions/test/mochitest/test_ext_background_generated_url.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_background_generated_url.html
@@ -22,17 +22,17 @@ add_task(function* test_url_of_generated
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       background: {
         scripts: ["bg.js"],
       },
       web_accessible_resources: ["_generated_background_page.html"],
     },
     files: {
-      "bg.js": `(${backgroundScript})();`,
+      "bg.js": backgroundScript,
     },
   });
 
   yield extension.startup();
   const EXPECTED_URL = yield extension.awaitMessage("script done");
 
   let win = window.open(EXPECTED_URL);
   ok(win, "Should open new tab at URL: " + EXPECTED_URL);

--- a/toolkit/components/extensions/test/mochitest/test_ext_background_teardown.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_background_teardown.html
@@ -9,30 +9,30 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
 </head>
 <body>
 
 <script>
 "use strict";
 
 add_task(function* test_background_reload_and_unload() {
-  function backgroundScript() {
+  function background() {
     browser.test.onMessage.addListener(msg => {
       browser.test.assertEq("reload-background", msg);
       location.reload();
     });
     browser.test.sendMessage("background-url", location.href);
   }
 
   let chromeScript = SpecialPowers.loadChromeScript(
       SimpleTest.getTestFileURL("file_teardown_test.js"));
   yield chromeScript.promiseOneMessage("chromescript-startup");
 
   let extensionData = {
-    background: `(${backgroundScript})();`,
+    background,
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   function* getContextEvents() {
     chromeScript.sendAsyncMessage("get-context-events");
     let contextEvents = yield chromeScript.promiseOneMessage("context-events");
     return contextEvents.filter(event => event.extensionId == extension.id);
   }

--- a/toolkit/components/extensions/test/mochitest/test_ext_contentscript.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_contentscript.html
@@ -9,17 +9,17 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_contentscript() {
-  function backgroundScript() {
+  function background() {
     browser.runtime.onMessage.addListener(([msg, expectedState, readyState], sender) => {
       if (msg == "chrome-namespace-ok") {
         browser.test.sendMessage(msg);
         return;
       }
 
       browser.test.assertEq(msg, "script-run", "message type is correct");
       browser.test.assertEq(readyState, expectedState, "readyState is correct");
@@ -64,23 +64,23 @@ add_task(function* test_contentscript() 
         },
         {
           "matches": ["http://mochi.test/*/file_sample.html"],
           "js": ["content_script.js"],
           "run_at": "document_idle",
         },
       ],
     },
-    background: "(" + backgroundScript.toString() + ")()",
+    background,
 
     files: {
-      "content_script_start.js": "(" + contentScriptStart.toString() + ")()",
-      "content_script_end.js": "(" + contentScriptEnd.toString() + ")()",
-      "content_script_idle.js": "(" + contentScriptIdle.toString() + ")()",
-      "content_script.js": "(" + contentScript.toString() + ")()",
+      "content_script_start.js": contentScriptStart,
+      "content_script_end.js": contentScriptEnd,
+      "content_script_idle.js": contentScriptIdle,
+      "content_script.js": contentScript,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   let loadingCount = 0;
   let interactiveCount = 0;
   let completeCount = 0;

--- a/toolkit/components/extensions/test/mochitest/test_ext_contentscript_api_injection.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_contentscript_api_injection.html
@@ -47,18 +47,18 @@ add_task(function* test_contentscript_ap
         },
       ],
       "web_accessible_resources": [
         "content_script_iframe.html",
       ],
     },
 
     files: {
-      "content_script.js": "new " + contentScript,
-      "content_script_iframe.js": "new " + contentScriptIframe,
+      "content_script.js": contentScript,
+      "content_script_iframe.js": contentScriptIframe,
       "content_script_iframe.html": document.querySelector("#test-asset").textContent,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   let awaitConsole = new Promise(resolve => {
     let chromeScript = SpecialPowers.loadChromeScript(

--- a/toolkit/components/extensions/test/mochitest/test_ext_contentscript_context.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_contentscript_context.html
@@ -31,17 +31,17 @@ add_task(function* test_contentscript_co
     manifest: {
       content_scripts: [{
         "matches": ["http://example.com/"],
         "js": ["content_script.js"],
       }],
     },
 
     files: {
-      "content_script.js": `(${contentScript})()`,
+      "content_script.js": contentScript,
     },
   });
 
   yield extension.startup();
 
   let win = window.open("http://example.com/");
   yield extension.awaitMessage("content-script-ready");
   yield extension.awaitMessage("content-script-show");

--- a/toolkit/components/extensions/test/mochitest/test_ext_contentscript_create_iframe.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_contentscript_create_iframe.html
@@ -20,17 +20,17 @@
     </head>
   </html>
 </textarea>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_contentscript_create_iframe() {
-  function backgroundScript() {
+  function background() {
     browser.runtime.onMessage.addListener((msg, sender) => {
       let {name, availableAPIs, manifest, testGetManifest} = msg;
       let hasExtTabsAPI = availableAPIs.indexOf("tabs") > 0;
       let hasExtWindowsAPI = availableAPIs.indexOf("windows") > 0;
 
       browser.test.assertFalse(hasExtTabsAPI, "the created iframe should not be able to use privileged APIs (tabs)");
       browser.test.assertFalse(hasExtWindowsAPI, "the created iframe should not be able to use privileged APIs (windows)");
 
@@ -92,22 +92,22 @@ add_task(function* test_contentscript_cr
           "run_at": "document_idle",
         },
       ],
       web_accessible_resources: [
         "content_script_iframe.html",
       ],
     },
 
-    background: "(" + backgroundScript + ")()",
+    background,
 
     files: {
-      "content_script.js": "new " + contentScript,
+      "content_script.js": contentScript,
       "content_script_iframe.html": document.querySelector("#test-asset").textContent,
-      "content_script_iframe.js": "new " + contentScriptIframe,
+      "content_script_iframe.js": contentScriptIframe,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   let contentScriptIframeCreatedPromise = new Promise(resolve => {
     extension.onMessage("content-script-iframe-loaded", () => { resolve(); });
   });

--- a/toolkit/components/extensions/test/mochitest/test_ext_contentscript_devtools_metadata.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_contentscript_devtools_metadata.html
@@ -13,17 +13,17 @@
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_contentscript_devtools_sandbox_metadata() {
   function contentScript() {
     browser.runtime.sendMessage("contentScript.executed");
   }
 
-  function backgroundScript() {
+  function background() {
     browser.runtime.onMessage.addListener((msg) => {
       if (msg == "contentScript.executed") {
         browser.test.notifyPass("contentScript.executed");
       }
     });
   }
 
   let extensionData = {
@@ -32,19 +32,19 @@ add_task(function* test_contentscript_de
         {
           "matches": ["http://mochi.test/*/file_sample.html"],
           "js": ["content_script.js"],
           "run_at": "document_idle",
         },
       ],
     },
 
-    background: "new " + backgroundScript,
+    background,
     files: {
-      "content_script.js": "new " + contentScript,
+      "content_script.js": contentScript,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   yield extension.startup();
 
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_contentscript_exporthelpers.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_contentscript_exporthelpers.html
@@ -69,17 +69,17 @@ add_task(function* test_contentscript_ex
       content_scripts: [{
         js: ["contentscript.js"],
         matches: ["http://mochi.test/*/file_sample.html"],
         run_at: "document_start",
       }],
     },
 
     files: {
-      "contentscript.js": `(${contentScript})();`,
+      "contentscript.js": contentScript,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   yield extension.startup();
 
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_contentscript_teardown.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_contentscript_teardown.html
@@ -12,36 +12,36 @@
 
 <script>
 "use strict";
 
 add_task(function* test_contentscript_reload_and_unload() {
   function contentScript() {
     browser.test.sendMessage("contentscript-run");
   }
-  function backgroundScript() {
+  function background() {
     let removedTabs = 0;
     browser.tabs.onRemoved.addListener(() => {
       browser.test.assertEq(1, ++removedTabs,
           "Expected only one tab to be removed during the test");
       browser.test.sendMessage("tab-closed");
     });
   }
 
   let extensionData = {
-    background: `(${backgroundScript})();`,
+    background,
     manifest: {
       content_scripts: [{
         "matches": ["http://mochi.test/*/file_sample.html"],
         "js": ["contentscript.js"],
       }],
     },
 
     files: {
-      "contentscript.js": `(${contentScript})();`,
+      "contentscript.js": contentScript,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   let chromeScript = SpecialPowers.loadChromeScript(
       SimpleTest.getTestFileURL("file_teardown_test.js"));

--- a/toolkit/components/extensions/test/mochitest/test_ext_cookies.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_cookies.html
@@ -9,17 +9,17 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_cookies() {
-  function backgroundScript() {
+  function background() {
     function assertExpected(expected, cookie) {
       for (let key of Object.keys(cookie)) {
         browser.test.assertTrue(key in expected, `found property ${key}`);
         browser.test.assertEq(expected[key], cookie[key], `property value for ${key} is correct`);
       }
       browser.test.assertEq(Object.keys(expected).length, Object.keys(cookie).length, "all expected properties found");
     }
 
@@ -163,17 +163,17 @@ add_task(function* test_cookies() {
       browser.test.assertEq("", cookie.name, "default name set");
       browser.test.assertEq("", cookie.value, "default value set");
       browser.test.assertEq(true, cookie.session, "no expiry date created session cookie");
       browser.test.notifyPass("cookies");
     });
   }
 
   let extension = ExtensionTestUtils.loadExtension({
-    background: `(${backgroundScript})()`,
+    background,
     manifest: {
       permissions: ["cookies", "*://example.org/"],
     },
   });
 
   yield extension.startup();
   info("extension loaded");
   yield extension.awaitFinish("cookies");

--- a/toolkit/components/extensions/test/mochitest/test_ext_cookies_expiry.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_cookies_expiry.html
@@ -37,17 +37,17 @@ add_task(function* test_cookies_expiry()
     }, 1000);
   }
 
   let domain = ".example.com";
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       "permissions": ["http://example.com/", "cookies"],
     },
-    background: `(${background})()`,
+    background,
   });
 
   let cookieSvc = SpecialPowers.Services.cookies;
 
   let cookie = {
     host: domain,
     name: "first",
     path: "/",

--- a/toolkit/components/extensions/test/mochitest/test_ext_exclude_include_globs.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_exclude_include_globs.html
@@ -9,17 +9,17 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_contentscript() {
-  function backgroundScript() {
+  function background() {
     browser.runtime.onMessage.addListener(([script], sender) => {
       browser.test.sendMessage("run", {script});
       browser.test.sendMessage("run-" + script);
     });
     browser.test.sendMessage("running");
   }
 
   function contentScriptAll() {
@@ -48,22 +48,22 @@ add_task(function* test_contentscript() 
         },
         {
           "matches": ["http://example.org/", "http://*.example.org/"],
           "exclude_globs": ["*test1*"],
           "js": ["content_script_excludes_test1.js"],
         },
       ],
     },
-    background: "(" + backgroundScript.toString() + ")()",
+    background,
 
     files: {
-      "content_script_all.js": "(" + contentScriptAll.toString() + ")()",
-      "content_script_includes_test1.js": "(" + contentScriptIncludesTest1.toString() + ")()",
-      "content_script_excludes_test1.js": "(" + contentScriptExcludesTest1.toString() + ")()",
+      "content_script_all.js": contentScriptAll,
+      "content_script_includes_test1.js": contentScriptIncludesTest1,
+      "content_script_excludes_test1.js": contentScriptExcludesTest1,
     },
 
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   let ran = 0;
   extension.onMessage("run", ({script}) => {

--- a/toolkit/components/extensions/test/mochitest/test_ext_generate.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_generate.html
@@ -8,31 +8,31 @@
   <script type="text/javascript" src="head.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
-function backgroundScript() {
+function background() {
   browser.test.log("running background script");
 
   browser.test.onMessage.addListener((x, y) => {
     browser.test.assertEq(x, 10, "x is 10");
     browser.test.assertEq(y, 20, "y is 20");
 
     browser.test.notifyPass("background test passed");
   });
 
   browser.test.sendMessage("running", 1);
 }
 
 let extensionData = {
-  background: "(" + backgroundScript.toString() + ")()",
+  background,
 };
 
 add_task(function* test_background() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   info("load complete");
   let [, x] = yield Promise.all([extension.startup(), extension.awaitMessage("running")]);
   is(x, 1, "got correct value from extension");
   info("startup complete");

--- a/toolkit/components/extensions/test/mochitest/test_ext_geturl.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_geturl.html
@@ -8,17 +8,17 @@
   <script type="text/javascript" src="head.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
-function backgroundScript() {
+function background() {
   browser.runtime.onMessage.addListener(([url1, url2]) => {
     let url3 = browser.runtime.getURL("test_file.html");
     let url4 = browser.extension.getURL("test_file.html");
 
     browser.test.assertTrue(url1 !== undefined, "url1 defined");
 
     browser.test.assertTrue(url1.startsWith("moz-extension://"), "url1 has correct scheme");
     browser.test.assertTrue(url1.endsWith("test_file.html"), "url1 has correct leaf name");
@@ -33,27 +33,27 @@ function backgroundScript() {
 
 function contentScript() {
   let url1 = browser.runtime.getURL("test_file.html");
   let url2 = browser.extension.getURL("test_file.html");
   browser.runtime.sendMessage([url1, url2]);
 }
 
 let extensionData = {
-  background: "(" + backgroundScript.toString() + ")()",
+  background,
   manifest: {
     "content_scripts": [{
       "matches": ["http://mochi.test/*/file_sample.html"],
       "js": ["content_script.js"],
       "run_at": "document_idle",
     }],
   },
 
   files: {
-    "content_script.js": "(" + contentScript.toString() + ")()",
+    "content_script.js": contentScript,
   },
 };
 
 add_task(function* test_contentscript() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_i18n.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_i18n.html
@@ -208,20 +208,20 @@ add_task(function* test_get_accept_langu
     manifest: {
       "content_scripts": [{
         "matches": ["http://mochi.test/*/file_sample.html"],
         "run_at": "document_start",
         "js": ["content_script.js"],
       }],
     },
 
-    background: `(${background})()`,
+    background,
 
     files: {
-      "content_script.js": `(${content})()`,
+      "content_script.js": content,
     },
   });
 
   let win = window.open("file_sample.html");
 
   yield extension.startup();
   yield extension.awaitMessage("ready");
 
@@ -326,17 +326,17 @@ add_task(function* test_detect_language(
     "of winkels nie en slegs oornagbesoekers word toegelaat bateleur";
   // String with intermixed French/English text
   const fr_en_string = "France is the largest country in Western Europe and the third-largest in Europe as a whole. " +
     "A accès aux chiens et aux frontaux qui lui ont été il peut consulter et modifier ses collections et exporter " +
     "Cet article concerne le pays européen aujourd’hui appelé République française. Pour d’autres usages du nom France, " +
     "Pour une aide rapide et effective, veuiller trouver votre aide dans le menu ci-dessus." +
     "Motoring events began soon after the construction of the first successful gasoline-fueled automobiles. The quick brown fox jumped over the lazy dog";
 
-  function backgroundScript() {
+  function background() {
     function checkResult(source, result, expected) {
       browser.test.assertEq(expected.isReliable, result.isReliable, "result.confident is true");
       browser.test.assertEq(
         expected.languages.length,
         result.languages.length,
         `result.languages contains the expected number of languages in ${source}`);
       expected.languages.forEach((lang, index) => {
         browser.test.assertEq(
@@ -382,20 +382,20 @@ add_task(function* test_detect_language(
     manifest: {
       "content_scripts": [{
         "matches": ["http://mochi.test/*/file_sample.html"],
         "run_at": "document_start",
         "js": ["content_script.js"],
       }],
     },
 
-    background: `(${backgroundScript})()`,
+    background,
 
     files: {
-      "content_script.js": `(${content})()`,
+      "content_script.js": content,
     },
   });
 
   let win = window.open("file_sample.html");
 
   yield extension.startup();
   yield extension.awaitMessage("ready");
 

--- a/toolkit/components/extensions/test/mochitest/test_ext_i18n_css.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_i18n_css.html
@@ -10,17 +10,17 @@
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_i18n_css() {
   let extension = ExtensionTestUtils.loadExtension({
-    background: "new " + function() {
+    background: function() {
       function fetch(url) {
         return new Promise((resolve, reject) => {
           let xhr = new XMLHttpRequest();
           xhr.open("GET", url);
           xhr.onload = () => { resolve(xhr.responseText); };
           xhr.onerror = reject;
           xhr.send();
         });

--- a/toolkit/components/extensions/test/mochitest/test_ext_inIncognitoContext_window.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_inIncognitoContext_window.html
@@ -23,23 +23,22 @@ add_task(function* test_in_incognito_con
     browser.windows.create({url: browser.runtime.getURL("/tab.html"), incognito: true});
   }
 
   function tabScript() {
     browser.runtime.sendMessage(browser.extension.inIncognitoContext);
   }
 
   let extension = ExtensionTestUtils.loadExtension({
-    background: `(${background})()`,
-    manifest: {},
+    background,
     files: {
-      "tab.js": `(${tabScript})()`,
+      "tab.js": tabScript,
       "tab.html": `<!DOCTYPE html><html><head>
         <meta charset="utf-8">
-        <script src="tab.js"></${"script"}>
+        <script src="tab.js"><\/script>
       </head></html>`,
     },
   });
 
   yield extension.startup();
   yield extension.awaitFinish("inIncognitoContext");
   yield extension.unload();
 });

--- a/toolkit/components/extensions/test/mochitest/test_ext_jsversion.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_jsversion.html
@@ -13,49 +13,49 @@
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_versioned_js() {
   // We need to deal with escaping the close script tags.
   // May as well consolidate it into one place.
-  let script = attrs => `<script ${attrs}></${"script"}>`;
+  let script = attrs => `<script ${attrs}><\/script>`;
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       "background": {"page": "background.html"},
     },
 
     files: {
       "background.html": `
         <meta charset="utf-8">
         ${script('src="background.js" type="application/javascript"')}
         ${script('src="background-1.js" type="application/javascript;version=1.8"')}
         ${script('src="background-2.js" type="application/javascript;version=latest"')}
         ${script('src="background-3.js" type="application/javascript"')}
       `,
 
-      "background.js": "new " + function() {
+      "background.js": function() {
         window.reportResult = msg => {
           browser.test.assertEq(
             msg, "background-script-3",
             "Expected a message only from the unversioned background script.");
 
           browser.test.sendMessage("finished");
         };
       },
 
-      "background-1.js": "new " + function() {
+      "background-1.js": function() {
         window.reportResult("background-script-1");
       },
-      "background-2.js": "new " + function() {
+      "background-2.js": function() {
         window.reportResult("background-script-2");
       },
-      "background-3.js": "new " + function() {
+      "background-3.js": function() {
         window.reportResult("background-script-3");
       },
     },
   });
 
   let messages = [/Versioned JavaScript.*not supported in WebExtension.*developer\.mozilla\.org/,
                   /Versioned JavaScript.*not supported in WebExtension.*developer\.mozilla\.org/];
 

--- a/toolkit/components/extensions/test/mochitest/test_ext_notifications.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_notifications.html
@@ -14,44 +14,44 @@
 
 // A 1x1 PNG image.
 // Source: https://commons.wikimedia.org/wiki/File:1x1.png (Public Domain)
 let image = atob("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEUAA" +
                  "ACnej3aAAAAAXRSTlMAQObYZgAAAApJREFUCNdjYAAAAAIAAeIhvDMAAAAASUVORK5CYII=");
 const IMAGE_ARRAYBUFFER = Uint8Array.from(image, byte => byte.charCodeAt(0)).buffer;
 
 add_task(function* test_notification() {
-  function backgroundScript() {
+  function background() {
     let opts = {
       type: "basic",
       title: "Testing Notification",
       message: "Carry on",
     };
 
     browser.notifications.create(opts).then(id => {
       browser.test.sendMessage("running", id);
       browser.test.notifyPass("background test passed");
     });
   }
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["notifications"],
     },
-    background: `(${backgroundScript})()`,
+    background,
   });
   yield extension.startup();
   let x = yield extension.awaitMessage("running");
   is(x, "0", "got correct id from notifications.create");
   yield extension.awaitFinish();
   yield extension.unload();
 });
 
 add_task(function* test_notification_events() {
-  function backgroundScript() {
+  function background() {
     let opts = {
       type: "basic",
       title: "Testing Notification",
       message: "Carry on",
     };
 
     // Test an ignored listener.
     browser.notifications.onButtonClicked.addListener(function() {});
@@ -72,29 +72,29 @@ add_task(function* test_notification_eve
       browser.test.sendMessage("running", id);
     });
   }
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["notifications"],
     },
-    background: `(${backgroundScript})()`,
+    background,
   });
   yield extension.startup();
   let x = yield extension.awaitMessage("closed");
   is(x, "5", "got correct id from onClosed listener");
   x = yield extension.awaitMessage("running");
   is(x, "5", "got correct id from notifications.create");
   yield extension.awaitFinish();
   yield extension.unload();
 });
 
 add_task(function* test_notification_clear() {
-  function backgroundScript() {
+  function background() {
     let opts = {
       type: "basic",
       title: "Testing Notification",
       message: "Carry on",
     };
 
     browser.notifications.onClosed.addListener(id => {
       browser.test.sendMessage("closed", id);
@@ -107,49 +107,49 @@ add_task(function* test_notification_cle
       browser.test.notifyPass("background test passed");
     });
   }
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["notifications"],
     },
-    background: `(${backgroundScript})()`,
+    background,
   });
   yield extension.startup();
   let x = yield extension.awaitMessage("closed");
   is(x, "99", "got correct id from onClosed listener");
   x = yield extension.awaitMessage("cleared");
   is(x, true, "got correct boolean from notifications.clear");
   yield extension.awaitFinish();
   yield extension.unload();
 });
 
 add_task(function* test_notifications_empty_getAll() {
-  function backgroundScript() {
+  function background() {
     browser.notifications.getAll().then(notifications => {
       browser.test.assertEq("object", typeof notifications, "getAll() returned an object");
       browser.test.assertEq(0, Object.keys(notifications).length, "the object has no properties");
       browser.test.notifyPass("getAll empty");
     });
   }
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["notifications"],
     },
-    background: `(${backgroundScript})()`,
+    background,
   });
   yield extension.startup();
   yield extension.awaitFinish("getAll empty");
   yield extension.unload();
 });
 
 add_task(function* test_notifications_populated_getAll() {
-  function backgroundScript() {
+  function background() {
     let opts = {
       type: "basic",
       iconUrl: "a.png",
       title: "Testing Notification",
       message: "Carry on",
     };
 
     browser.notifications.create("p1", opts).then(() => {
@@ -171,28 +171,28 @@ add_task(function* test_notifications_po
       browser.test.notifyPass("getAll populated");
     });
   }
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["notifications"],
     },
-    background: `(${backgroundScript})()`,
+    background,
     files: {
       "a.png": IMAGE_ARRAYBUFFER,
     },
   });
   yield extension.startup();
   yield extension.awaitFinish("getAll populated");
   yield extension.unload();
 });
 
 add_task(function* test_buttons_unsupported() {
-  function backgroundScript() {
+  function background() {
     let opts = {
       type: "basic",
       title: "Testing Notification",
       message: "Carry on",
       buttons: [{title: "Button title"}],
     };
 
     let exception = {};
@@ -208,17 +208,17 @@ add_task(function* test_buttons_unsuppor
     );
     browser.test.notifyPass("buttons-unsupported");
   }
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["notifications"],
     },
-    background: `(${backgroundScript})()`,
+    background,
   });
   yield extension.startup();
   yield extension.awaitFinish("buttons-unsupported");
   yield extension.unload();
 });
 
 </script>
 

--- a/toolkit/components/extensions/test/mochitest/test_ext_runtime_connect.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_runtime_connect.html
@@ -8,17 +8,17 @@
   <script type="text/javascript" src="head.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
-function backgroundScript() {
+function background() {
   browser.runtime.onConnect.addListener(port => {
     browser.test.assertEq(port.name, "ernie", "port name correct");
     browser.test.assertTrue(port.sender.url.endsWith("file_sample.html"), "URL correct");
     browser.test.assertTrue(port.sender.tab.url.endsWith("file_sample.html"), "tab URL correct");
 
     let expected = "message 1";
     port.onMessage.addListener(msg => {
       browser.test.assertEq(msg, expected, "message is expected");
@@ -43,28 +43,28 @@ function contentScript() {
     if (msg == "message 2") {
       port.postMessage("message 3");
       port.disconnect();
     }
   });
 }
 
 let extensionData = {
-  background: "(" + backgroundScript.toString() + ")()",
+  background,
   manifest: {
     "permissions": ["tabs"],
     "content_scripts": [{
       "matches": ["http://mochi.test/*/file_sample.html"],
       "js": ["content_script.js"],
       "run_at": "document_start",
     }],
   },
 
   files: {
-    "content_script.js": "(" + contentScript.toString() + ")()",
+    "content_script.js": contentScript,
   },
 };
 
 add_task(function* test_contentscript() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_runtime_connect_twoway.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_runtime_connect_twoway.html
@@ -9,17 +9,17 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
 </head>
 <body>
 
 <script>
 "use strict";
 
 add_task(function* test_connect_bidirectionally_and_postMessage() {
-  function backgroundScript() {
+  function background() {
     let onConnectCount = 0;
     browser.runtime.onConnect.addListener(port => {
       // 3. onConnect by connect() from CS.
       browser.test.assertEq("from-cs", port.name);
       browser.test.assertEq(1, ++onConnectCount,
           "BG onConnect should be called once");
 
       let tabId = port.sender.tab.id;
@@ -93,25 +93,25 @@ add_task(function* test_connect_bidirect
         "CS port.onMessage should be called once");
 
       // 10. should trigger port.onMessage in BG.
       port.postMessage("from CS to port");
     });
   }
 
   let extensionData = {
-    background: `(${backgroundScript})();`,
+    background,
     manifest: {
       content_scripts: [{
         js: ["contentscript.js"],
         matches: ["http://mochi.test/*/file_sample.html"],
       }],
     },
     files: {
-      "contentscript.js": `(${contentScript})();`,
+      "contentscript.js": contentScript,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
   info("extension loaded");
 
   yield extension.awaitMessage("ready");

--- a/toolkit/components/extensions/test/mochitest/test_ext_runtime_disconnect.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_runtime_disconnect.html
@@ -8,17 +8,17 @@
   <script type="text/javascript" src="head.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
-function backgroundScript() {
+function background() {
   browser.runtime.onConnect.addListener(port => {
     browser.test.assertEq(port.name, "ernie", "port name correct");
     port.onDisconnect.addListener(() => {
       // Closing an already-disconnected port is a no-op.
       port.disconnect();
       port.disconnect();
       browser.test.sendMessage("disconnected");
     });
@@ -26,28 +26,28 @@ function backgroundScript() {
   });
 }
 
 function contentScript() {
   browser.runtime.connect({name: "ernie"});
 }
 
 let extensionData = {
-  background: "(" + backgroundScript.toString() + ")()",
+  background,
   manifest: {
     "permissions": ["tabs"],
     "content_scripts": [{
       "matches": ["http://mochi.test/*/file_sample.html"],
       "js": ["content_script.js"],
       "run_at": "document_idle",
     }],
   },
 
   files: {
-    "content_script.js": "(" + contentScript.toString() + ")()",
+    "content_script.js": contentScript,
   },
 };
 
 add_task(function* test_contentscript() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_runtime_id.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_runtime_id.html
@@ -31,20 +31,20 @@ add_task(function* test_runtime_id() {
       applications: {gecko: {id}},
       "content_scripts": [{
         "matches": ["http://mochi.test/*/file_sample.html"],
         "run_at": "document_start",
         "js": ["content_script.js"],
       }],
     },
 
-    background: `(${background})()`,
+    background,
 
     files: {
-      "content_script.js": `(${content})()`,
+      "content_script.js": content,
     },
   });
 
   yield extension.startup();
 
   let backgroundId = yield extension.awaitMessage("background-id");
   is(backgroundId, id, "runtime.id from background script is correct");
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_sandbox_var.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_sandbox_var.html
@@ -8,41 +8,41 @@
   <script type="text/javascript" src="head.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
-function backgroundScript() {
+function background() {
   browser.runtime.onMessage.addListener(result => {
     browser.test.assertEq(result, 12, "x is 12");
     browser.test.notifyPass("background test passed");
   });
 }
 
 function contentScript() {
   window.x = 12;
   browser.runtime.onMessage.addListener(function() {});
   browser.runtime.sendMessage(window.x);
 }
 
 let extensionData = {
-  background: "(" + backgroundScript.toString() + ")()",
+  background,
   manifest: {
     "content_scripts": [{
       "matches": ["http://mochi.test/*/file_sample.html"],
       "js": ["content_script.js"],
       "run_at": "document_idle",
     }],
   },
 
   files: {
-    "content_script.js": "(" + contentScript.toString() + ")()",
+    "content_script.js": contentScript,
   },
 };
 
 add_task(function* test_contentscript() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_schema.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_schema.html
@@ -18,17 +18,17 @@ add_task(function* testEmptySchema() {
   function background() {
     browser.test.assertTrue(!("manifest" in browser), "browser.manifest is not defined");
     browser.test.assertTrue("storage" in browser, "browser.storage should be defined");
     browser.test.assertTrue(!("contextMenus" in browser), "browser.contextMenus should not be defined");
     browser.test.notifyPass("schema");
   }
 
   let extension = ExtensionTestUtils.loadExtension({
-    background: `(${background})()`,
+    background,
     manifest: {
       permissions: ["storage"],
     },
   });
 
   yield extension.startup();
   yield extension.awaitFinish("schema");
   yield extension.unload();
@@ -41,17 +41,17 @@ add_task(function* testUnknownProperties
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["unknownPermission"],
 
       unknown_property: {},
     },
 
-    background: `(${background})()`,
+    background,
   });
 
   let messages = [
     {message: /processing permissions\.0: Unknown permission "unknownPermission"/},
     {message: /processing unknown_property: An unexpected property was found in the WebExtension manifest/},
   ];
 
   let waitForConsole = new Promise(resolve => {

--- a/toolkit/components/extensions/test/mochitest/test_ext_sendmessage_doublereply.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_sendmessage_doublereply.html
@@ -8,17 +8,17 @@
   <script type="text/javascript" src="head.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
-function backgroundScript() {
+function background() {
   // Add two listeners that both send replies. We're supposed to ignore all but one
   // of them. Which one is chosen is non-deterministic.
 
   browser.runtime.onMessage.addListener((msg, sender, sendReply) => {
     browser.test.assertTrue(sender.tab.url.endsWith("file_sample.html"), "sender url correct");
 
     if (msg == "getreply") {
       sendReply("reply1");
@@ -62,28 +62,28 @@ function contentScript() {
     if (resp != "reply1" && resp != "reply2") {
       return; // test failed
     }
     browser.runtime.sendMessage("done");
   });
 }
 
 let extensionData = {
-  background: "(" + backgroundScript.toString() + ")()",
+  background,
   manifest: {
     "permissions": ["tabs"],
     "content_scripts": [{
       "matches": ["http://mochi.test/*/file_sample.html"],
       "js": ["content_script.js"],
       "run_at": "document_start",
     }],
   },
 
   files: {
-    "content_script.js": "(" + contentScript.toString() + ")()",
+    "content_script.js": contentScript,
   },
 };
 
 add_task(function* test_contentscript() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_sendmessage_no_receiver.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_sendmessage_no_receiver.html
@@ -17,17 +17,17 @@ function loadContentScriptExtension(cont
   let extensionData = {
     manifest: {
       "content_scripts": [{
         "js": ["contentscript.js"],
         "matches": ["http://mochi.test/*/file_sample.html"],
       }],
     },
     files: {
-      "contentscript.js": `(${contentScript})();`,
+      "contentscript.js": contentScript,
     },
   };
   return ExtensionTestUtils.loadExtension(extensionData);
 }
 
 add_task(function* test_content_script_sendMessage_without_listener() {
   function contentScript() {
     browser.runtime.sendMessage("msg").then(reply => {

--- a/toolkit/components/extensions/test/mochitest/test_ext_sendmessage_reply.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_sendmessage_reply.html
@@ -8,17 +8,17 @@
   <script type="text/javascript" src="head.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
-function backgroundScript() {
+function background() {
   browser.runtime.onMessage.addListener((msg, sender, sendReply) => {
     browser.test.assertTrue(sender.tab.url.endsWith("file_sample.html"), "sender url correct");
 
     if (msg == 0) {
       sendReply("reply1");
     } else if (msg == 1) {
       window.setTimeout(function() {
         sendReply("reply2");
@@ -40,28 +40,28 @@ function contentScript() {
         return; // test failed
       }
       browser.runtime.sendMessage(2);
     });
   });
 }
 
 let extensionData = {
-  background: "(" + backgroundScript.toString() + ")()",
+  background,
   manifest: {
     "permissions": ["tabs"],
     "content_scripts": [{
       "matches": ["http://mochi.test/*/file_sample.html"],
       "js": ["content_script.js"],
       "run_at": "document_idle",
     }],
   },
 
   files: {
-    "content_script.js": "(" + contentScript.toString() + ")()",
+    "content_script.js": contentScript,
   },
 };
 
 add_task(function* test_contentscript() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   let win = window.open("file_sample.html");

--- a/toolkit/components/extensions/test/mochitest/test_ext_storage_content.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_storage_content.html
@@ -174,17 +174,17 @@ let extensionData = {
       "js": ["content_script.js"],
       "run_at": "document_idle",
     }],
 
     permissions: ["storage"],
   },
 
   files: {
-    "content_script.js": "(" + contentScript.toString() + ")()",
+    "content_script.js": contentScript,
   },
 };
 
 add_task(function* test_contentscript() {
   let win = window.open("file_sample.html");
   yield waitForLoad(win);
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);

--- a/toolkit/components/extensions/test/mochitest/test_ext_storage_tab.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_storage_tab.html
@@ -81,28 +81,28 @@ add_task(function* test_multiple_pages()
         return browser.storage.local.set({key: {foo: {bar: "baz"}}});
       }
     });
 
     browser.runtime.sendMessage("tab-ready");
   }
 
   let extension = ExtensionTestUtils.loadExtension({
-    background: `(${background})()`,
+    background,
 
     files: {
       "tab.html": `<!DOCTYPE html>
         <html>
           <head>
             <meta charset="utf-8">
-            <script src="tab.js"></${"script"}>
+            <script src="tab.js"><\/script>
           </head>
         </html>`,
 
-      "tab.js": `(${tab})()`,
+      "tab.js": tab,
     },
 
     manifest: {
       permissions: ["storage"],
     },
   });
 
   yield extension.startup();

--- a/toolkit/components/extensions/test/mochitest/test_ext_subframes_privileges.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_subframes_privileges.html
@@ -9,17 +9,17 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_webext_tab_subframe_privileges() {
-  function backgroundScript() {
+  function background() {
     browser.runtime.onMessage.addListener(({msg, success, tabId, error}) => {
       if (msg == "webext-tab-subframe-privileges") {
         if (success) {
           browser.tabs.remove(tabId)
             .then(() => browser.test.notifyPass(msg));
         } else {
           browser.test.log(`Got an unexpected error: ${error}`);
           browser.tabs.query({active: true})
@@ -52,33 +52,33 @@ add_task(function* test_webext_tab_subfr
         msg: "webext-tab-subframe-privileges",
         success: false,
         error: `Privileged APIs missing in WebExtension tab sub-frame`,
       });
     }
   }
 
   let extensionData = {
-    background: "new " + backgroundScript,
+    background,
     files: {
       "tab.html": `<!DOCTYPE>
           <head>
             <meta charset="utf-8">
           </head>
           <body>
             <iframe src="tab-subframe.html"></iframe>
           </body>
         </html>`,
       "tab-subframe.html": `<!DOCTYPE>
           <head>
             <meta charset="utf-8">
-            <script src="tab-subframe.js"></${"script"}>
+            <script src="tab-subframe.js"><\/script>
           </head>
         </html>`,
-      "tab-subframe.js": `(${tabSubframeScript})()`,
+      "tab-subframe.js": tabSubframeScript,
     },
   };
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   yield extension.startup();
 
   yield extension.awaitFinish("webext-tab-subframe-privileges");
   yield extension.unload();
@@ -104,32 +104,32 @@ add_task(function* test_webext_backgroun
          </head>
          <body>
            <iframe src="background-subframe.html"></iframe>
          </body>
        </html>`,
       "background-subframe.html": `<!DOCTYPE>
          <head>
            <meta charset="utf-8">
-           <script src="background-subframe.js"></${"script"}>
+           <script src="background-subframe.js"><\/script>
          </head>
        </html>`,
-      "background-subframe.js": `(${backgroundSubframeScript})()`,
+      "background-subframe.js": backgroundSubframeScript,
     },
   };
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   yield extension.startup();
 
   yield extension.awaitFinish("webext-background-subframe-privileges");
   yield extension.unload();
 });
 
 add_task(function* test_webext_contentscript_iframe_subframe_privileges() {
-  function backgroundScript() {
+  function background() {
     browser.runtime.onMessage.addListener(({name, hasTabsAPI, hasStorageAPI}) => {
       if (name == "contentscript-iframe-loaded") {
         browser.test.assertFalse(hasTabsAPI,
                                  "Subframe of a content script privileged iframes has no access to privileged APIs");
         browser.test.assertTrue(hasStorageAPI,
                                  "Subframe of a content script privileged iframes has access to content script APIs");
 
         browser.test.notifyPass("webext-contentscript-subframe-privileges");
@@ -147,44 +147,44 @@ add_task(function* test_webext_contentsc
 
   function contentScript() {
     let iframe = document.createElement("iframe");
     iframe.setAttribute("src", browser.runtime.getURL("/contentscript-iframe.html"));
     document.body.appendChild(iframe);
   }
 
   let extensionData = {
-    background: "new " + backgroundScript,
+    background,
     manifest: {
       "permissions": ["storage"],
       "content_scripts": [{
         "matches": ["http://example.com/*"],
         "js": ["contentscript.js"],
       }],
       web_accessible_resources: [
         "contentscript-iframe.html",
       ],
     },
     files: {
-      "contentscript.js": `(${contentScript})()`,
+      "contentscript.js": contentScript,
       "contentscript-iframe.html": `<!DOCTYPE>
          <head>
            <meta charset="utf-8">
          </head>
          <body>
            <iframe src="contentscript-iframe-subframe.html"></iframe>
          </body>
        </html>`,
       "contentscript-iframe-subframe.html": `<!DOCTYPE>
          <head>
            <meta charset="utf-8">
-           <script src="contentscript-iframe-subframe.js"></${"script"}>
+           <script src="contentscript-iframe-subframe.js"><\/script>
          </head>
        </html>`,
-      "contentscript-iframe-subframe.js": `(${subframeScript})()`,
+      "contentscript-iframe-subframe.js": subframeScript,
     },
   };
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   yield extension.startup();
 
   let win = window.open("http://example.com");
 

--- a/toolkit/components/extensions/test/mochitest/test_ext_tab_teardown.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_tab_teardown.html
@@ -59,17 +59,17 @@ function* runTabReloadAndCloseTest(exten
       "ExtensionContext URL at closing tab should be tab URL");
 
   chromeScript.sendAsyncMessage("cleanup");
   chromeScript.destroy();
   yield extension.unload();
 }
 
 add_task(function* test_extension_page_tabs_create_reload_and_close() {
-  function backgroundScript() {
+  function background() {
     let tabId;
     browser.test.onMessage.addListener(msg => {
       if (msg === "open extension page") {
         chrome.tabs.create({url: "page.html"}, tab => {
           tabId = tab.id;
         });
       } else if (msg === "reload extension page") {
         chrome.tabs.reload(tabId);
@@ -81,35 +81,35 @@ add_task(function* test_extension_page_t
     });
   }
 
   function pageScript() {
     browser.test.sendMessage("extension page loaded", document.URL);
   }
 
   let extensionData = {
-    background: `(${backgroundScript})();`,
+    background,
     files: {
       "page.html": `<!DOCTYPE html><meta charset="utf-8"><script src="page.js"><\/script>`,
-      "page.js": `(${pageScript})();`,
+      "page.js": pageScript,
     },
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
   yield* runTabReloadAndCloseTest(extension);
 });
 
 add_task(function* test_extension_page_window_open_reload_and_close() {
   // This tests whether a context that is opened via window.open is properly
   // disposed when the tab closes.
   // The background page cannot use window.open (bugzil.la/1282021), so we open
   // another extension page that manages the window.open-tab for testing.
-  function backgroundScript() {
+  function background() {
     chrome.tabs.create({url: "window.open.html"});
   }
 
   function windowOpenScript() {
     let win;
     browser.test.onMessage.addListener(msg => {
       if (msg === "open extension page") {
         win = window.open("page.html");
@@ -126,22 +126,22 @@ add_task(function* test_extension_page_w
     browser.test.sendMessage("setup-intermediate-tab");
   }
 
   function pageScript() {
     browser.test.sendMessage("extension page loaded", document.URL);
   }
 
   let extensionData = {
-    background: `(${backgroundScript})();`,
+    background,
     files: {
       "page.html": `<!DOCTYPE html><meta charset="utf-8"><script src="page.js"><\/script>`,
-      "page.js": `(${pageScript})();`,
+      "page.js": pageScript,
       "window.open.html": `<!DOCTYPE html><meta charset="utf-8"><script src="window.open.js"><\/script>`,
-      "window.open.js": `(${windowOpenScript})();`,
+      "window.open.js": windowOpenScript,
     },
   };
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
   yield extension.awaitMessage("setup-intermediate-tab");
   yield* runTabReloadAndCloseTest(extension);
 });
 </script>

--- a/toolkit/components/extensions/test/mochitest/test_ext_web_accessible_resources.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_web_accessible_resources.html
@@ -136,43 +136,43 @@ add_task(function* test_web_accessible_r
       ],
 
       "web_accessible_resources": [
         "/accessible.html",
         "wild*.html",
       ],
     },
 
-    background: `(${background})()`,
+    background,
 
     files: {
-      "content_script.js": `(${contentScript})()`,
+      "content_script.js": contentScript,
 
       "accessible.html": `<html><head>
         <meta charset="utf-8">
-        <script src="accessible.js"></${"script"}>
+        <script src="accessible.js"><\/script>
       </head></html>`,
 
       "accessible.js": 'browser.runtime.sendMessage(["page-script", location.href]);',
 
       "inaccessible.html": `<html><head>
         <meta charset="utf-8">
-        <script src="inaccessible.js"></${"script"}>
+        <script src="inaccessible.js"><\/script>
       </head></html>`,
 
       "inaccessible.js": 'browser.runtime.sendMessage(["page-script", location.href]);',
 
       "wild1.html": `<html><head>
         <meta charset="utf-8">
-        <script src="wild.js"></${"script"}>
+        <script src="wild.js"><\/script>
       </head></html>`,
 
       "wild2.htm": `<html><head>
         <meta charset="utf-8">
-        <script src="wild.js"></${"script"}>
+        <script src="wild.js"><\/script>
       </head></html>`,
 
       "wild.js": 'browser.runtime.sendMessage(["page-script", location.href]);',
     },
   });
 
   yield extension.startup();
 
@@ -226,21 +226,21 @@ add_task(function* test_web_accessible_r
         "run_at": "document_start",
         "js": ["content_script_helper.js", "content_script.js"],
       }],
       "web_accessible_resources": [
         "image.png",
         "test_script.js",
       ],
     },
-    background: `(${background})()`,
+    background,
     files: {
       "content_script_helper.js": `${testImageLoading}`,
-      "content_script.js": `(${content})()`,
-      "test_script.js": `(${testScript})()`,
+      "content_script.js": content,
+      "test_script.js": testScript,
       "image.png": IMAGE_ARRAYBUFFER,
     },
   });
 
   // This is used to watch the blocked data bounce off CSP.
   function examiner() {
     SpecialPowers.addObserver(this, "csp-on-violate-policy", false);
   }
@@ -321,21 +321,21 @@ add_task(function* test_web_accessible_r
         "run_at": "document_start",
         "js": ["content_script_helper.js", "content_script.js"],
       }],
       "web_accessible_resources": [
         "image.png",
         "test_script.js",
       ],
     },
-    background: `(${background})()`,
+    background,
     files: {
       "content_script_helper.js": `${testImageLoading}`,
-      "content_script.js": `(${content})()`,
-      "test_script.js": `(${testScript})()`,
+      "content_script.js": content,
+      "test_script.js": testScript,
       "image.png": IMAGE_ARRAYBUFFER,
     },
   });
 
   SpecialPowers.setBoolPref("security.mixed_content.block_display_content", true);
 
   yield Promise.all([extension.startup(), extension.awaitMessage("background-ready")]);
 

--- a/toolkit/components/extensions/test/mochitest/test_ext_webnavigation.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_webnavigation.html
@@ -127,17 +127,17 @@ add_task(function* webnav_transitions_pr
   }
 
   let extensionData = {
     manifest: {
       permissions: [
         "webNavigation",
       ],
     },
-    background: `(${backgroundScriptTransitions})()`,
+    background: backgroundScriptTransitions,
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   extension.onMessage("received", ({url, event, details}) => {
     received.push({url, event, details});
 
     if (event == waitingEvent && url == waitingURL) {
@@ -344,17 +344,17 @@ add_task(function* webnav_transitions_pr
 
 add_task(function* webnav_ordering() {
   let extensionData = {
     manifest: {
       permissions: [
         "webNavigation",
       ],
     },
-    background: "(" + backgroundScript.toString() + ")()",
+    background: backgroundScript,
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   extension.onMessage("received", ({url, event}) => {
     received.push({url, event});
 
     if (event == waitingEvent && url == waitingURL) {
@@ -510,17 +510,17 @@ add_task(function* webnav_error_event() 
   }
 
   let extensionData = {
     manifest: {
       permissions: [
         "webNavigation",
       ],
     },
-    background: `(${backgroundScriptErrorEvent})()`,
+    background: backgroundScriptErrorEvent,
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   extension.onMessage("received", ({url, event, details}) => {
     received.push({url, event, details});
 
     if (event == waitingEvent && url == waitingURL) {

--- a/toolkit/components/extensions/test/mochitest/test_ext_webnavigation_filters.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_webnavigation_filters.html
@@ -9,17 +9,17 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 </head>
 <body>
 
 <script type="text/javascript">
 "use strict";
 
 add_task(function* test_webnav_unresolved_uri_on_expected_URI_scheme() {
-  function backgroundScript() {
+  function background() {
     let lastTest;
 
     function cleanupTestListeners() {
       if (lastTest) {
         let {event, okListener, failListener} = lastTest;
         lastTest = null;
         browser.test.log(`Cleanup previous test event listeners`);
         browser.webNavigation[event].removeListener(okListener);
@@ -65,17 +65,17 @@ add_task(function* test_webnav_unresolve
   }
 
   let extensionData = {
     manifest: {
       permissions: [
         "webNavigation",
       ],
     },
-    background: "new " + backgroundScript,
+    background,
   };
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
 
   yield extension.startup();
 
   yield extension.awaitMessage("ready");
 
@@ -252,17 +252,17 @@ add_task(function* test_webnav_unresolve
   info("WebNavigation event filters test scenarios completed.");
 
   yield extension.unload();
 
   win.close();
 });
 
 add_task(function* test_webnav_empty_filter_validation_error() {
-  function backgroundScript() {
+  function background() {
     let catchedException;
 
     try {
       browser.webNavigation.onCompleted.addListener(
         // Empty callback (not really used)
         () => {},
         // Empty filter (which should raise a validation error exception).
         {url: []}
@@ -282,17 +282,17 @@ add_task(function* test_webnav_empty_fil
   }
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: [
         "webNavigation",
       ],
     },
-    background: "new " + backgroundScript,
+    background,
   });
 
   yield extension.startup();
 
   yield extension.awaitFinish("webNav.emptyFilterValidationError");
 
   yield extension.unload();
 });