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

lib/elemHideFF.js

Index: lib/elemHideFF.js
===================================================================
--- a/lib/elemHideFF.js
+++ b/lib/elemHideFF.js
@@ -12,16 +12,18 @@
  * 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");
 
@@ -34,17 +36,37 @@ FilterNotifier.on("elemhideupdate", () =
     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+    // long as only outdated Firefox versions are affected.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)