Issue 5381 - iterate stylesheet with an array subscript

chrome/content/elemHideEmulation.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 385 matching lines @@
   addSelectors(stylesheets)
   {
     let selectors = [];
     let selectorFilters = [];
 
     let elements = [];
     let elementFilters = [];
 
     let cssStyles = [];
 
-    for (let stylesheet of stylesheets)
+    // Chrome < 51 doesn't have an iterable StyleSheetList
+    // https://issues.adblockplus.org/ticket/5381
+    for (let i = 0; i < stylesheets.length; i++)
     {
+      let stylesheet = stylesheets[i];
       // Explicitly ignore third-party stylesheets to ensure consistent behavior
       // between Firefox and Chrome.
       if (!this.isSameOrigin(stylesheet))
         continue;
 
       let rules = stylesheet.cssRules;
       if (!rules)
         continue;
 
       for (let rule of rules)
@@ skipping 53 matching lines @@
 
       if (this.patterns.length > 0)
       {
         let {document} = this.window;
         this.addSelectors(document.styleSheets);
         document.addEventListener("load", this.onLoad.bind(this), true);
       }
     });
   }
 };