Issue 3108 - Less hacky approach to disabling E10S compatibility shims

lib/utils.js

Index: lib/utils.js
===================================================================
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -375,16 +375,32 @@ let Utils = exports.Utils =
   getParams: function()
   {
     let ret = sidebarParams;
     sidebarParams = null;
     return ret;
   },
 
   /**
+   * E10S compatibility shims will reroute property retrieval on some objects
+   * in order to enable custom behavior. This cannot be disabled on case by case
+   * basis (see https://bugzilla.mozilla.org/show_bug.cgi?id=1167802). So
+   * instead we use a different execution context to retrieve properties when
+   * E10S compatibility shims shouldn't kick in. This method simply returns
+   * obj[prop] but without any custom behavior.
+   */
+  getPropertyWithoutCompatShims: function(/**Object*/ obj, /**String*/ prop)
+  {
+    let sandbox = Cu.Sandbox(Utils.systemPrincipal);
+    sandbox.obj = obj;
+    sandbox.prop = prop;
+    return Cu.evalInSandbox("obj[prop]", sandbox);
+  },
+
+  /**
    * Verifies RSA signature. The public key and signature should be base64-encoded.
    * @param {string} key
    * @param {string} signature
    * @param {string} data
    * @return {boolean}
    */
   verifySignature: function(key, signature, data)
   {