Issue 5347 - Check for contextMenus API support

ext/background.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 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 405 matching lines @@
   };
 
 
   /* Context menus */
 
   let contextMenuItems = new ext.PageMap();
   let contextMenuUpdating = false;
 
   let updateContextMenu = () =>
   {
-    if (contextMenuUpdating)
+    // Firefox for Android does not support context menus.
+    // https://bugzilla.mozilla.org/show_bug.cgi?id=1269062
+    if (!("contextMenus" in chrome) || contextMenuUpdating)
       return;
 
     contextMenuUpdating = true;
 
     chrome.tabs.query({active: true, lastFocusedWindow: true}, tabs =>
     {
       chrome.contextMenus.removeAll(() =>
       {
         contextMenuUpdating = false;
 
@@ skipping 302 matching lines @@
   ext.windows = {
     create(createData, callback)
     {
       chrome.windows.create(createData, createdWindow =>
       {
         afterTabLoaded(callback)(createdWindow.tabs[0]);
       });
     }
   };
 }());