--- a/toolkit/components/extensions/test/mochitest/file_script_good.js
+++ b/toolkit/components/extensions/test/mochitest/file_script_good.js
@@ -1,3 +1,12 @@
 "use strict";
 
 window.success = window.success ? window.success + 1 : 1;
+
+{
+  let scripts = document.getElementsByTagName("script");
+  let url = new URL(scripts[scripts.length - 1].src);
+  let flag = url.searchParams.get("q");
+  if (flag) {
+    window.postMessage(flag, "*");
+  }
+}

--- a/toolkit/components/extensions/test/mochitest/mochitest-common.ini
+++ b/toolkit/components/extensions/test/mochitest/mochitest-common.ini
@@ -120,17 +120,17 @@ skip-if = os == 'android' && debug # bug
 [test_ext_webnavigation.html]
 skip-if = os == 'android' && debug # bug 1397615
 [test_ext_webnavigation_filters.html]
 skip-if = (os == 'android' && debug) || (verify && (os == 'linux' || os == 'mac')) # bug 1397615
 [test_ext_webrequest_auth.html]
 skip-if = os == 'android'
 [test_ext_webrequest_background_events.html]
 [test_ext_webrequest_basic.html]
-skip-if = os == 'android' && debug || (os == 'linux' && !asan) # bug 1397615, bug 1455405
+skip-if = os == 'android' && debug # bug 1397615
 [test_ext_webrequest_errors.html]
 [test_ext_webrequest_filter.html]
 skip-if = os == 'android' && debug # bug 1452348
 [test_ext_webrequest_frameId.html]
 [test_ext_webrequest_hsts.html]
 skip-if = os == 'android' || os == 'linux' # linux, bug 1398120
 [test_ext_webrequest_upgrade.html]
 [test_ext_webrequest_upload.html]

--- a/toolkit/components/extensions/test/mochitest/test_ext_webrequest_basic.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_webrequest_basic.html
@@ -7,20 +7,24 @@
   <script type="text/javascript" src="/tests/SimpleTest/AddTask.js"></script>
   <script type="text/javascript" src="/tests/SimpleTest/ExtensionTestUtils.js"></script>
   <script type="text/javascript" src="head_webrequest.js"></script>
   <script type="text/javascript" src="head.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 <script>
 "use strict";
 
-function spinEventLoop() {
-  return new Promise((resolve, reject) => {
-    window.requestIdleCallback(() => {
-      resolve();
+function promiseWindowEvent(name, accept) {
+  return new Promise(resolve => {
+    window.addEventListener(name, function listener(event) {
+      if (event.data !== accept) {
+        return;
+      }
+      window.removeEventListener(name, listener);
+      resolve(event);
     });
   });
 }
 
 if (AppConstants.platform === "android") {
   SimpleTest.requestLongerTimeout(3);
 }
 
@@ -75,21 +79,16 @@ add_task(async function test_webRequest_
   };
   extension.sendMessage("set-expected", {expect, origin: location.href});
   await extension.awaitMessage("continue");
   addStylesheet("file_style_bad.css");
   await extension.awaitMessage("cancelled");
   // we redirect to style_good which completes the test
   addStylesheet("file_style_redirect.css");
   await extension.awaitMessage("done");
-
-  // waiting for CSS applied.
-  await spinEventLoop();
-  let style = window.getComputedStyle(document.getElementById("test"));
-  is(style.getPropertyValue("color"), "rgb(255, 0, 0)", "Good CSS loaded");
 });
 
 add_task(async function test_webRequest_images() {
   let expect = {
     "file_image_bad.png": {
       type: "image",
       events: ["onBeforeRequest", "onErrorOccurred"],
       cancel: "onBeforeRequest",
@@ -127,26 +126,24 @@ add_task(async function test_webRequest_
       redirect: "file_script_good.js",
     },
     "file_script_good.js": {
       type: "script",
     },
   };
   extension.sendMessage("set-expected", {expect, origin: location.href});
   await extension.awaitMessage("continue");
+  let message = promiseWindowEvent("message", "test1");
   addScript("file_script_bad.js");
   await extension.awaitMessage("cancelled");
   // we redirect to script_good which completes the test
-  addScript("file_script_redirect.js");
+  addScript("file_script_redirect.js?q=test1");
   await extension.awaitMessage("done");
 
-  // wait for JS executed
-  await spinEventLoop();
-  is(window.success, 1, "Good script ran");
-  is(window.failure, undefined, "Failure script didn't run");
+  is((await message).data, "test1", "good script ran");
 });
 
 add_task(async function test_webRequest_xhr_get() {
   let expect = {
     "file_script_xhr.js": {
       type: "script",
     },
     "xhr_resource": {
@@ -190,26 +187,26 @@ add_task(async function test_webRequest_
     "nonexistent_script_url.js": {
       status: 404,
       type: "script",
       cached: false,
     },
   };
   extension.sendMessage("set-expected", {expect, origin: location.href});
   await extension.awaitMessage("continue");
+  let message = promiseWindowEvent("message", "test1");
+
   addImage("file_image_good.png");
-  addScript("file_script_good.js");
+  addScript("file_script_good.js?q=test1");
+
+  is((await message).data, "test1", "good script ran");
+
   addStylesheet("file_style_good.css");
   addScript("nonexistent_script_url.js");
   await extension.awaitMessage("done");
-
-  // wait for JS executed
-  await spinEventLoop();
-  is(window.success, 2, "Good script ran");
-  is(window.failure, undefined, "Failure script didn't run");
 });
 
 add_task(async function test_webRequest_headers() {
   let expect = {
     "file_script_nonexistent.js": {
       type: "script",
       status: 404,
       headers: {