Issue 4353 - Remove deprecated __proto__ syntax

chrome/content/tests/subscriptionClasses.js

 (function()
 {
   module("Subscription classes", {setup: prepareFilterComponents, teardown: restoreFilterComponents});
 
   function compareSubscription(url, expected, postInit)
   {
     expected.push("[Subscription]")
     let subscription = Subscription.fromURL(url);
     if (postInit)
       postInit(subscription)
     let result = [];
     subscription.serialize(result);
     equal(result.sort().join("\n"), expected.sort().join("\n"), url);
 
-    let map = {__proto__: null};
+    let map = Object.create(null);
     for (let line of result.slice(1))
     {
       if (/(.*?)=(.*)/.test(line))
         map[RegExp.$1] = RegExp.$2;
     }
     let subscription2 = Subscription.fromObject(map);
     equal(subscription.toString(), subscription2.toString(), url + " deserialization");
   }
 
   test("Subscription class definitions", function()
@@ skipping 29 matching lines @@
       subscription.version = 24
       subscription.requiredVersion = "0.6";
     });
     compareSubscription("~wl~", ["url=~wl~", "disabled=true", "title=Test group"], function(subscription)
     {
       subscription.title = "Test group";
       subscription.disabled = true;
     });
   });
 })();