Issue 6183 - Reduce "Receiving end does not exist" exceptions

lib/filterComposer.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 300 matching lines @@
     baseURL: message.baseURL,
     page: sender.page,
     frame: sender.frame
   });
 });
 
 port.on("composer.quoteCSS", (message, sender) =>
 {
   return quoteCSS(message.CSS);
 });
-
-ext.pages.onLoading.addListener(page =>
-{
-  // A newly opened tab that is still loading has its URL set to about:blank
-  if (/^https?:/.test(page.url.protocol))
-    page.sendMessage({type: "composer.content.finished"});
-});