Issue 4198 - Don't send Map objects in messages when using Firefox 40 and below

lib/elemHideFF.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
+let {Services} = Cu.import("resource://gre/modules/Services.jsm", {});
+
 let {port} = require("messaging");
 let {ElemHide} = require("elemHide");
 let {FilterNotifier} = require("filterNotifier");
 let {FilterStorage} = require("filterStorage");
 let {Prefs} = require("prefs");
 let {Policy} = require("contentPolicy");
 let {Utils} = require("utils");
 
 let isDirty = false;
 FilterNotifier.on("elemhideupdate", () =>
 {
   // Notify content process asynchronously, only one message per update batch.
   if (!isDirty)
   {
     isDirty = true;
     Utils.runAsync(() => {
       isDirty = false;
       port.emit("elemhideupdate")
     });
   }
 });
 
-port.on("getSelectors", () => ElemHide.getSelectors());
+let translateMap = map => map;
+if (Services.vc.compare(Utils.platformVersion, "40.0") <= 0)
+{
+  translateMap = map =>
+  {
+    // We cannot send Map objects with Gecko 40 and below, "translate" them
+    // into nested arrays. This isn't very efficient but that should be ok as
+    // long as only outdated Firefox versions are affected.
+    let translated = [];
+    for (let [key, value] of map)
+    {
+      if (value instanceof Map)
+        translated.push([key, translateMap(value)]);
+      else
+        translated.push([key, value]);
+    }
+    return translated;
+  };
+}
+
+port.on("getSelectors", () => translateMap(ElemHide.getSelectors()));
 
 port.on("elemhideEnabled", ({frames, isPrivate}) =>
 {
   if (!Prefs.enabled)
     return {enabled: false};
 
   let hit = Policy.isFrameWhitelisted(frames, true);
   if (hit)
   {
     let [frameIndex, contentType, docDomain, thirdParty, location, filter] = hit;
     if (contentType != "GENERICHIDE")
     {
       if (!isPrivate)
         FilterStorage.increaseHitCount(filter);
       return {
         enabled: false,
         contentType, docDomain, thirdParty, location,
         filter: filter.text, filterType: filter.type
       };
     }
   }
 
   return {enabled: true};
 });