diff --git a/devtools/client/webconsole/enhancers/css-error-reporting.js b/devtools/client/webconsole/enhancers/css-error-reporting.js
index 6d58ba764ef8..76f0b2d8429d 100644
--- a/devtools/client/webconsole/enhancers/css-error-reporting.js
+++ b/devtools/client/webconsole/enhancers/css-error-reporting.js
@@ -7,7 +7,7 @@
 const {
   INITIALIZE,
   FILTER_TOGGLE,
-  FILTERS,
+  TARGET_AVAILABLE,
 } = require("devtools/client/webconsole/constants");
 
 /**
@@ -15,23 +15,30 @@ const {
  * filter is toggled on.
  */
 function ensureCSSErrorReportingEnabled(webConsoleUI) {
-  let watchingCSSMessages = false;
   return next => (reducer, initialState, enhancer) => {
     function ensureErrorReportingEnhancer(state, action) {
-      state = reducer(state, action);
+      const proxies = webConsoleUI ? webConsoleUI.getAllProxies() : null;
+      if (!proxies) {
+        return reducer(state, action);
+      }
 
-      // If we're already watching CSS messages, or if the CSS filter is disabled,
-      // we don't do anything.
-      if (!webConsoleUI || watchingCSSMessages || !state.filters.css) {
+      state = reducer(state, action);
+      if (!state.filters.css) {
         return state;
       }
 
       const cssFilterToggled =
-        action.type == FILTER_TOGGLE && action.filter == FILTERS.CSS;
-
-      if (cssFilterToggled || action.type == INITIALIZE) {
-        watchingCSSMessages = true;
-        webConsoleUI.watchCssMessages();
+        action.type == FILTER_TOGGLE && action.filter == "css";
+      if (
+        cssFilterToggled ||
+        action.type == INITIALIZE ||
+        action.type == TARGET_AVAILABLE
+      ) {
+        for (const proxy of proxies) {
+          if (proxy.target && proxy.target.ensureCSSErrorReportingEnabled) {
+            proxy.target.ensureCSSErrorReportingEnabled();
+          }
+        }
       }
 
       return state;
diff --git a/devtools/client/webconsole/test/browser/browser_webconsole_cached_messages.js b/devtools/client/webconsole/test/browser/browser_webconsole_cached_messages.js
index e6a58aecd9aa..8627ad777a4f 100644
--- a/devtools/client/webconsole/test/browser/browser_webconsole_cached_messages.js
+++ b/devtools/client/webconsole/test/browser/browser_webconsole_cached_messages.js
@@ -59,7 +59,7 @@ add_task(async function() {
   info("Log different type of messages to fill the cache");
   await logMessages();
 
-  info("Select the console");
+  info("Open the console");
   hud = await openConsole();
 
   await testMessagesVisibility(hud);
@@ -177,9 +177,8 @@ async function testMessagesVisibility(hud, checkNetworkMessage = true) {
   }
 
   // We can't assert the CSS warning position, so we only check that it's visible.
-  await waitFor(
-    () => findMessage(hud, "cssColorBug611032", ".message.warn.css"),
-    "Couldn't find the CSS warning message"
+  await waitFor(() =>
+    findMessage(hud, "cssColorBug611032", ".message.warn.css")
   );
   ok(true, "css warning message is visible");
 }
diff --git a/devtools/client/webconsole/test/browser/browser_webconsole_filters_persist.js b/devtools/client/webconsole/test/browser/browser_webconsole_filters_persist.js
index 8d1a7b228fa8..dc2778402db5 100644
--- a/devtools/client/webconsole/test/browser/browser_webconsole_filters_persist.js
+++ b/devtools/client/webconsole/test/browser/browser_webconsole_filters_persist.js
@@ -43,10 +43,6 @@ add_task(async function() {
   filterButtons.forEach(filterButton => {
     ok(filterIsEnabled(filterButton), "filter is enabled");
   });
-
-  // Wait for the CSS warning to be displayed so we don't have a pending promise.
-  await waitFor(() => findMessage(hud, "Expected color but found ‘blouge’"));
-
   // Check that the ui settings were persisted.
   await closeTabAndToolbox();
 });
diff --git a/devtools/client/webconsole/test/browser/browser_webconsole_stubs_css_message.js b/devtools/client/webconsole/test/browser/browser_webconsole_stubs_css_message.js
index 11e49c666601..ca93070d0e74 100644
--- a/devtools/client/webconsole/test/browser/browser_webconsole_stubs_css_message.js
+++ b/devtools/client/webconsole/test/browser/browser_webconsole_stubs_css_message.js
@@ -66,19 +66,20 @@ async function generateCssMessageStubs() {
   // The resource-watcher only supports a single call to watch/unwatch per
   // instance, so we attach a unique watch callback, which will forward the
   // resource to `handleErrorMessage`, dynamically updated for each command.
-  let handleCSSMessage = function() {};
+  let handleErrorMessage = function() {};
 
-  const onCSSMessageAvailable = ({ resource }) => {
-    handleCSSMessage(resource);
+  const onErrorMessageAvailable = ({ resource }) => {
+    handleErrorMessage(resource);
   };
 
-  await resourceWatcher.watchResources([resourceWatcher.TYPES.CSS_MESSAGE], {
-    onAvailable: onCSSMessageAvailable,
+  /* CSS errors are considered as pageError on the server */
+  await resourceWatcher.watchResources([resourceWatcher.TYPES.ERROR_MESSAGE], {
+    onAvailable: onErrorMessageAvailable,
   });
 
   for (const code of getCommands()) {
     const received = new Promise(resolve => {
-      handleCSSMessage = function(packet) {
+      handleErrorMessage = function(packet) {
         const key = packet.pageError.errorMessage;
         stubs.set(key, getCleanedPacket(key, packet));
         resolve();
@@ -97,8 +98,8 @@ async function generateCssMessageStubs() {
     await received;
   }
 
-  resourceWatcher.unwatchResources([resourceWatcher.TYPES.CSS_MESSAGE], {
-    onAvailable: onCSSMessageAvailable,
+  resourceWatcher.unwatchResources([resourceWatcher.TYPES.ERROR_MESSAGE], {
+    onAvailable: onErrorMessageAvailable,
   });
 
   await closeTabAndToolbox().catch(() => {});
diff --git a/devtools/client/webconsole/test/node/fixtures/stubs/cssMessage.js b/devtools/client/webconsole/test/node/fixtures/stubs/cssMessage.js
index 922d11e2630c..6e150f848762 100644
--- a/devtools/client/webconsole/test/node/fixtures/stubs/cssMessage.js
+++ b/devtools/client/webconsole/test/node/fixtures/stubs/cssMessage.js
@@ -37,11 +37,11 @@ rawPackets.set(`Unknown property ‘such-unknown-property’.  Declaration dropp
     "stacktrace": null,
     "notes": null,
     "chromeContext": false,
+    "cssSelectors": "p",
     "isPromiseRejection": false,
     "isForwardedFromContentProcess": false
   },
-  "resourceType": "css-message",
-  "cssSelectors": "p"
+  "resourceType": "error-message"
 });
 
 rawPackets.set(`Error in parsing value for ‘padding-top’.  Declaration dropped.`, {
@@ -63,11 +63,11 @@ rawPackets.set(`Error in parsing value for ‘padding-top’.  Declaration dropp
     "stacktrace": null,
     "notes": null,
     "chromeContext": false,
+    "cssSelectors": "p",
     "isPromiseRejection": false,
     "isForwardedFromContentProcess": false
   },
-  "resourceType": "css-message",
-  "cssSelectors": "p"
+  "resourceType": "error-message"
 });
 
 
diff --git a/devtools/client/webconsole/test/node/helpers.js b/devtools/client/webconsole/test/node/helpers.js
index 48cc7558bb18..cc3929bda093 100644
--- a/devtools/client/webconsole/test/node/helpers.js
+++ b/devtools/client/webconsole/test/node/helpers.js
@@ -143,7 +143,6 @@ function getWebConsoleUiMock(hud, proxyOverrides) {
     toolbox: {
       sessionId: 1,
     },
-    watchCssMessages: () => {},
   };
 }
 
diff --git a/devtools/client/webconsole/utils/messages.js b/devtools/client/webconsole/utils/messages.js
index 15b77e76c776..4144027a1b1d 100644
--- a/devtools/client/webconsole/utils/messages.js
+++ b/devtools/client/webconsole/utils/messages.js
@@ -111,10 +111,6 @@ function transformResource(resource) {
       return transformPageErrorResource(resource);
     }
 
-    case ResourceWatcher.TYPES.CSS_MESSAGE: {
-      return transformCSSMessageResource(resource);
-    }
-
     case "networkEvent": {
       return transformNetworkEventResource(resource);
     }
@@ -309,7 +305,7 @@ function transformPlatformMessageResource(platformMessageResource) {
   });
 }
 
-function transformPageErrorResource(pageErrorResource, override = {}) {
+function transformPageErrorResource(pageErrorResource) {
   const { pageError, targetFront } = pageErrorResource;
   let level = MESSAGE_LEVEL.ERROR;
   if (pageError.warning) {
@@ -327,37 +323,30 @@ function transformPageErrorResource(pageErrorResource, override = {}) {
       }
     : null;
 
-  return new ConsoleMessage(
-    Object.assign(
-      {
-        targetFront,
-        innerWindowID: pageError.innerWindowID,
-        source: MESSAGE_SOURCE.JAVASCRIPT,
-        type: MESSAGE_TYPE.LOG,
-        level,
-        category: pageError.category,
-        messageText: pageError.errorMessage,
-        stacktrace: pageError.stacktrace ? pageError.stacktrace : null,
-        frame,
-        errorMessageName: pageError.errorMessageName,
-        exceptionDocURL: pageError.exceptionDocURL,
-        hasException: pageError.hasException,
-        parameters: pageError.hasException ? [pageError.exception] : null,
-        timeStamp: pageError.timeStamp,
-        notes: pageError.notes,
-        private: pageError.private,
-        chromeContext: pageError.chromeContext,
-        isPromiseRejection: pageError.isPromiseRejection,
-      },
-      override
-    )
-  );
-}
-
-function transformCSSMessageResource(cssMessageResource) {
-  return transformPageErrorResource(cssMessageResource, {
-    cssSelectors: cssMessageResource.cssSelectors,
-    source: MESSAGE_SOURCE.CSS,
+  const matchesCSS = pageError.category == "CSS Parser";
+  const messageSource = matchesCSS
+    ? MESSAGE_SOURCE.CSS
+    : MESSAGE_SOURCE.JAVASCRIPT;
+  return new ConsoleMessage({
+    targetFront,
+    innerWindowID: pageError.innerWindowID,
+    source: messageSource,
+    type: MESSAGE_TYPE.LOG,
+    level,
+    category: pageError.category,
+    messageText: pageError.errorMessage,
+    stacktrace: pageError.stacktrace ? pageError.stacktrace : null,
+    frame,
+    errorMessageName: pageError.errorMessageName,
+    exceptionDocURL: pageError.exceptionDocURL,
+    hasException: pageError.hasException,
+    parameters: pageError.hasException ? [pageError.exception] : null,
+    timeStamp: pageError.timeStamp,
+    notes: pageError.notes,
+    private: pageError.private,
+    chromeContext: pageError.chromeContext,
+    cssSelectors: pageError.cssSelectors,
+    isPromiseRejection: pageError.isPromiseRejection,
   });
 }
 
diff --git a/devtools/client/webconsole/webconsole-ui.js b/devtools/client/webconsole/webconsole-ui.js
index 516446642df4..b56c81816930 100644
--- a/devtools/client/webconsole/webconsole-ui.js
+++ b/devtools/client/webconsole/webconsole-ui.js
@@ -346,23 +346,13 @@ class WebConsoleUI {
     );
   }
 
-  async watchCssMessages() {
-    const { resourceWatcher } = this.hud;
-    await resourceWatcher.watchResources([resourceWatcher.TYPES.CSS_MESSAGE], {
-      onAvailable: this._onResourceAvailable,
-    });
-  }
-
   _onResourceAvailable({ resourceType, targetFront, resource }) {
-    const { TYPES } = this.hud.resourceWatcher;
     // Ignore messages forwarded from content processes if we're in fission browser toolbox.
     if (
-      !this.wrapper ||
-      ((resourceType === TYPES.ERROR_MESSAGE ||
-        resourceType === TYPES.CSS_MESSAGE) &&
-        resource.pageError?.isForwardedFromContentProcess &&
-        (this.isBrowserToolboxConsole || this.isBrowserConsole) &&
-        this.fissionSupport)
+      resourceType === this.hud.resourceWatcher.TYPES.ERROR_MESSAGE &&
+      resource.pageError.isForwardedFromContentProcess &&
+      (this.isBrowserToolboxConsole || this.isBrowserConsole) &&
+      this.fissionSupport
     ) {
       return;
     }
diff --git a/devtools/server/actors/targets/browsing-context.js b/devtools/server/actors/targets/browsing-context.js
index 990ca33e55d4..ae26e8d870e1 100644
--- a/devtools/server/actors/targets/browsing-context.js
+++ b/devtools/server/actors/targets/browsing-context.js
@@ -1230,8 +1230,7 @@ const browsingContextTargetPrototype = {
   /**
    * Ensure that CSS error reporting is enabled.
    */
-  async ensureCSSErrorReportingEnabled(request) {
-    const promises = [];
+  ensureCSSErrorReportingEnabled(request) {
     for (const docShell of this.docShells) {
       if (docShell.cssErrorReportingEnabled) {
         continue;
@@ -1254,15 +1253,12 @@ const browsingContextTargetPrototype = {
           continue;
         }
         // Reparse the sheet so that we see the existing errors.
-        const onStyleSheetParsed = getSheetText(sheet, this._consoleActor)
-          .then(text => {
-            InspectorUtils.parseStyleSheet(sheet, text, /* aUpdate = */ false);
-          })
-          .catch(e => console.error("Error while parsing stylesheet"));
-        promises.push(onStyleSheetParsed);
+        getSheetText(sheet, this._consoleActor).then(text => {
+          InspectorUtils.parseStyleSheet(sheet, text, /* aUpdate = */ false);
+        });
       }
     }
-    await Promise.all(promises);
+
     return {};
   },
 
diff --git a/devtools/shared/resources/legacy-listeners/css-messages.js b/devtools/shared/resources/legacy-listeners/css-messages.js
deleted file mode 100644
index 893dd4b34e1d..000000000000
--- a/devtools/shared/resources/legacy-listeners/css-messages.js
+++ /dev/null
@@ -1,77 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-"use strict";
-
-const {
-  ResourceWatcher,
-} = require("devtools/shared/resources/resource-watcher");
-
-module.exports = async function({
-  targetList,
-  targetFront,
-  isFissionEnabledOnContentToolbox,
-  onAvailable,
-}) {
-  // Allow the top level target if the targetFront has an `ensureCSSErrorREportingEnabled`
-  // function. Also allow frame in non-content toolbox and in content toolbox when the
-  // fission toolbox pref is set.
-  const isContentToolbox = targetList.targetFront.isLocalTab;
-  const listenForFrames = !isContentToolbox || isFissionEnabledOnContentToolbox;
-  const isAllowed =
-    typeof targetFront.ensureCSSErrorReportingEnabled == "function" &&
-    (targetFront.isTopLevel ||
-      (targetFront.targetType === targetList.TYPES.FRAME && listenForFrames));
-
-  if (!isAllowed) {
-    return;
-  }
-
-  const webConsoleFront = await targetFront.getFront("console");
-
-  // Request notifying about new CSS messages (they're emitted from the "PageError listener").
-  await webConsoleFront.startListeners(["PageError"]);
-
-  // Fetch already existing messages
-  // /!\ The actor implementation requires to call startListeners("PageError") first /!\
-  const { messages } = await webConsoleFront.getCachedMessages(["PageError"]);
-
-  const cachedMessages = [];
-  for (let message of messages) {
-    if (message.pageError?.category !== "CSS Parser") {
-      continue;
-    }
-
-    // Handling cached messages for servers older than Firefox 78.
-    // Wrap the message into a `pageError` attribute, to match `pageError` behavior
-    if (message._type) {
-      message = {
-        pageError: message,
-      };
-    }
-    message.resourceType = ResourceWatcher.TYPES.CSS_MESSAGE;
-    message.cssSelectors = message.pageError.cssSelectors;
-    delete message.pageError.cssSelectors;
-    cachedMessages.push(message);
-  }
-
-  onAvailable(cachedMessages);
-
-  // Calling ensureCSSErrorReportingEnabled will make the server parse the stylesheets to
-  // retrieve the warnings if the docShell wasn't already watching for CSS messages.
-  await targetFront.ensureCSSErrorReportingEnabled();
-
-  // CSS Messages are emited fron the PageError listener, which also send regular errors
-  // that we need to filter out.
-  webConsoleFront.on("pageError", message => {
-    if (message.pageError.category !== "CSS Parser") {
-      return;
-    }
-
-    message.resourceType = ResourceWatcher.TYPES.CSS_MESSAGE;
-    message.cssSelectors = message.pageError.cssSelectors;
-    delete message.pageError.cssSelectors;
-    onAvailable([message]);
-  });
-};
diff --git a/devtools/shared/resources/legacy-listeners/error-messages.js b/devtools/shared/resources/legacy-listeners/error-messages.js
index dee36d4a68e9..2910bc78deab 100644
--- a/devtools/shared/resources/legacy-listeners/error-messages.js
+++ b/devtools/shared/resources/legacy-listeners/error-messages.js
@@ -44,13 +44,11 @@ module.exports = async function({
 
   // On older server (< v77), we're also getting LogMessage cached messages, so we need
   // to ignore those.
-  // On server < v79, we're also getting CSS Messages that we need to filter out.
   messages = messages.filter(message => {
     return (
-      (webConsoleFront.traits.newCacheStructure ||
-        !message._type ||
-        message._type == "PageError") &&
-      message.pageError.category !== "CSS Parser"
+      webConsoleFront.traits.newCacheStructure ||
+      !message._type ||
+      message._type == "PageError"
     );
   });
 
@@ -71,11 +69,6 @@ module.exports = async function({
   onAvailable(messages);
 
   webConsoleFront.on("pageError", message => {
-    // On server < v79, we're getting CSS Messages that we need to filter out.
-    if (message.pageError.category === "CSS Parser") {
-      return;
-    }
-
     message.resourceType = ResourceWatcher.TYPES.ERROR_MESSAGE;
     onAvailable([message]);
   });
diff --git a/devtools/shared/resources/legacy-listeners/moz.build b/devtools/shared/resources/legacy-listeners/moz.build
index dad8dd062971..7e6ab7557426 100644
--- a/devtools/shared/resources/legacy-listeners/moz.build
+++ b/devtools/shared/resources/legacy-listeners/moz.build
@@ -5,7 +5,6 @@
 DevToolsModules(
     'console-messages.js',
     'css-changes.js',
-    'css-messages.js',
     'error-messages.js',
     'platform-messages.js',
     'root-node.js',
diff --git a/devtools/shared/resources/resource-watcher.js b/devtools/shared/resources/resource-watcher.js
index f5c350b3c4c4..814c9c2a5c45 100644
--- a/devtools/shared/resources/resource-watcher.js
+++ b/devtools/shared/resources/resource-watcher.js
@@ -422,7 +422,6 @@ class ResourceWatcher {
 ResourceWatcher.TYPES = ResourceWatcher.prototype.TYPES = {
   CONSOLE_MESSAGE: "console-message",
   CSS_CHANGE: "css-change",
-  CSS_MESSAGE: "css-message",
   ERROR_MESSAGE: "error-message",
   PLATFORM_MESSAGE: "platform-message",
   DOCUMENT_EVENT: "document-event",
@@ -438,8 +437,6 @@ const LegacyListeners = {
     .CONSOLE_MESSAGE]: require("devtools/shared/resources/legacy-listeners/console-messages"),
   [ResourceWatcher.TYPES
     .CSS_CHANGE]: require("devtools/shared/resources/legacy-listeners/css-changes"),
-  [ResourceWatcher.TYPES
-    .CSS_MESSAGE]: require("devtools/shared/resources/legacy-listeners/css-messages"),
   [ResourceWatcher.TYPES
     .ERROR_MESSAGE]: require("devtools/shared/resources/legacy-listeners/error-messages"),
   [ResourceWatcher.TYPES
diff --git a/devtools/shared/resources/tests/browser.ini b/devtools/shared/resources/tests/browser.ini
index e3b788b2a269..9d59162a8547 100644
--- a/devtools/shared/resources/tests/browser.ini
+++ b/devtools/shared/resources/tests/browser.ini
@@ -16,7 +16,6 @@ support-files =
 [browser_resources_client_caching.js]
 [browser_resources_console_messages.js]
 [browser_resources_css_changes.js]
-[browser_resources_css_messages.js]
 [browser_resources_document_events.js]
 [browser_resources_error_messages.js]
 [browser_resources_platform_messages.js]
diff --git a/devtools/shared/resources/tests/browser_resources_css_messages.js b/devtools/shared/resources/tests/browser_resources_css_messages.js
deleted file mode 100644
index 545fbe56b31a..000000000000
--- a/devtools/shared/resources/tests/browser_resources_css_messages.js
+++ /dev/null
@@ -1,196 +0,0 @@
-/* Any copyright is dedicated to the Public Domain.
-   http://creativecommons.org/publicdomain/zero/1.0/ */
-
-"use strict";
-
-// Test the ResourceWatcher API around CSS_MESSAGE
-// Reproduces the CSS message assertions from devtools/shared/webconsole/test/chrome/test_page_errors.html
-
-const {
-  ResourceWatcher,
-} = require("devtools/shared/resources/resource-watcher");
-
-// Create a simple server so we have a nice sourceName in the resources packets.
-const httpServer = createTestHTTPServer();
-httpServer.registerPathHandler(`/test_css_messages.html`, (req, res) => {
-  res.setStatusLine(req.httpVersion, 200, "OK");
-  res.write(`<meta charset=utf8>
-    <style>
-      html {
-        color: bloup;
-      }
-    </style>Test CSS Messages`);
-});
-
-const TEST_URI = `http://localhost:${httpServer.identity.primaryPort}/test_css_messages.html`;
-
-add_task(async function testWatchingCssMessages() {
-  // Disable the preloaded process as it creates processes intermittently
-  // which forces the emission of RDP requests we aren't correctly waiting for.
-  await pushPref("dom.ipc.processPrelaunch.enabled", false);
-
-  // Open a test tab
-  const tab = await addTab(TEST_URI);
-
-  const {
-    client,
-    resourceWatcher,
-    targetList,
-  } = await initResourceWatcherAndTarget(tab);
-
-  const receivedMessages = [];
-  const { onAvailable, onAllMessagesReceived } = setupOnAvailableFunction(
-    targetList,
-    receivedMessages
-  );
-  await resourceWatcher.watchResources([ResourceWatcher.TYPES.CSS_MESSAGE], {
-    onAvailable,
-  });
-
-  info(
-    "Now log CSS warning *after* the call to ResourceWatcher.watchResources and after " +
-      "having received the existing message"
-  );
-  // We need to wait for the first CSS Warning as it is not a cached message; when we
-  // start watching, the `cssErrorReportingEnabled` is checked on the target docShell, and
-  // if it is false, we re-parse the stylesheets to get the messages.
-  await BrowserTestUtils.waitForCondition(() => receivedMessages.length === 1);
-
-  info("Trigger a CSS Warning");
-  triggerCSSWarning(tab);
-
-  info("Waiting for all expected CSS messages to be received");
-  await onAllMessagesReceived;
-  ok(true, "All the expected CSS messages were received");
-
-  Services.console.reset();
-  targetList.stopListening();
-  await client.close();
-});
-
-add_task(async function testWatchingCachedCssMessages() {
-  // Disable the preloaded process as it creates processes intermittently
-  // which forces the emission of RDP requests we aren't correctly waiting for.
-  await pushPref("dom.ipc.processPrelaunch.enabled", false);
-
-  // Open a test tab
-  const tab = await addTab(TEST_URI);
-
-  // By default, the CSS Parser does not emit warnings at all, for performance matter.
-  // Since we actually want the Parser to emit those messages _before_ we start listening
-  // for CSS messages, we need to set the cssErrorReportingEnabled flag on the docShell.
-  await SpecialPowers.spawn(gBrowser.selectedBrowser, [], function() {
-    content.docShell.cssErrorReportingEnabled = true;
-  });
-
-  // Setting the docShell flag only indicates to the Parser that from now on, it should
-  // emit warnings. But it does not automatically emit warnings for the existing CSS
-  // errors in the stylesheets. So here we reload the tab, which will make the Parser
-  // parse the stylesheets again, this time emitting warnings.
-  const loaded = BrowserTestUtils.browserLoaded(tab.linkedBrowser);
-  tab.linkedBrowser.reload();
-  // wait for the tab to be fully loaded
-  await loaded;
-  // and trigger more CSS warnings
-  await triggerCSSWarning(tab);
-
-  // At this point, all messages should be in the ConsoleService cache, and we can begin
-  // to watch and check that we do retrieve those messages.
-  const {
-    client,
-    resourceWatcher,
-    targetList,
-  } = await initResourceWatcherAndTarget(tab);
-
-  const receivedMessages = [];
-  const { onAvailable } = setupOnAvailableFunction(
-    targetList,
-    receivedMessages
-  );
-  await resourceWatcher.watchResources([ResourceWatcher.TYPES.CSS_MESSAGE], {
-    onAvailable,
-  });
-  is(receivedMessages.length, 3, "Cached messages were retrieved as expected");
-
-  Services.console.reset();
-  targetList.stopListening();
-  await client.close();
-});
-
-function setupOnAvailableFunction(targetList, receivedMessages) {
-  // The expected messages are the CSS warnings:
-  // - one for the rule in the style element
-  // - two for the JS modified style we're doing in the test.
-  const expectedMessages = [
-    {
-      pageError: {
-        errorMessage: /Expected color but found ‘bloup’/,
-        sourceName: /test_css_messages/,
-        category: "CSS Parser",
-        timeStamp: /^\d+$/,
-        error: false,
-        warning: true,
-      },
-      cssSelectors: "html",
-    },
-    {
-      pageError: {
-        errorMessage: /Error in parsing value for ‘width’/,
-        sourceName: /test_css_messages/,
-        category: "CSS Parser",
-        timeStamp: /^\d+$/,
-        error: false,
-        warning: true,
-      },
-    },
-    {
-      pageError: {
-        errorMessage: /Error in parsing value for ‘height’/,
-        sourceName: /test_css_messages/,
-        category: "CSS Parser",
-        timeStamp: /^\d+$/,
-        error: false,
-        warning: true,
-      },
-    },
-  ];
-
-  let done;
-  const onAllMessagesReceived = new Promise(resolve => (done = resolve));
-  const onAvailable = ({ resourceType, targetFront, resource }) => {
-    const { pageError } = resource;
-
-    is(
-      resource.targetFront,
-      targetList.targetFront,
-      "The targetFront property is the expected one"
-    );
-
-    if (!pageError.sourceName.includes("test_css_messages")) {
-      info(`Ignore error from unknown source: "${pageError.sourceName}"`);
-      return;
-    }
-
-    const index = receivedMessages.length;
-    receivedMessages.push(pageError);
-
-    info(`checking received css message #${index}: ${pageError.errorMessage}`);
-    ok(pageError, "The resource has a pageError attribute");
-    checkObject(resource, expectedMessages[index]);
-
-    if (receivedMessages.length == expectedMessages.length) {
-      done();
-    }
-  };
-  return { onAvailable, onAllMessagesReceived };
-}
-
-/**
- * Sets invalid values for width and height on the document's body style attribute.
- */
-function triggerCSSWarning(tab) {
-  return ContentTask.spawn(tab.linkedBrowser, null, function frameScript() {
-    content.document.body.style.width = "red";
-    content.document.body.style.height = "blue";
-  });
-}