diff -r 000000000000 -r 6474c204b198 js/src/tests/ecma_5/extensions/proxy-__proto__.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/ecma_5/extensions/proxy-__proto__.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,81 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+var gTestfile = 'proxy-__proto__.js';
+var BUGNUMBER = 770344;
+var summary = "Behavior of __proto__ on proxies";
+
+print(BUGNUMBER + ": " + summary);
+
+/**************
+ * BEGIN TEST *
+ **************/
+
+var protoDesc = Object.getOwnPropertyDescriptor(Object.prototype, "__proto__");
+var protoGetter = protoDesc.get;
+var protoSetter = protoDesc.set;
+
+function pp(arr)
+{
+  return arr.map(function(v) { return "" + v; }).join(", ");
+}
+
+function testProxy(creator, args, proto)
+{
+  print("Now testing behavior for " +
+        "Proxy." + creator + "(" + pp(args) + ")");
+
+  var pobj = Proxy[creator].apply(Proxy, args);
+
+  // Check [[Prototype]] before attempted mutation
+  assertEq(Object.getPrototypeOf(pobj), proto);
+  assertEq(protoGetter.call(pobj), proto);
+
+  // Attempt [[Prototype]] mutation
+  protoSetter.call(pobj, null);
+
+  // Check [[Prototype]] after attempted mutation
+  assertEq(Object.getPrototypeOf(pobj), null);
+  assertEq(protoGetter.call(pobj), null);
+}
+
+// Proxy object with non-null [[Prototype]]
+var nonNullProto = { toString: function() { return "non-null prototype"; } };
+var nonNullHandler = { toString: function() { return "non-null handler"; } };
+testProxy("create", [nonNullHandler, nonNullProto], nonNullProto);
+
+// Proxy object with null [[Prototype]]
+var nullProto = null;
+var nullHandler = { toString: function() { return "null handler"; } };
+testProxy("create", [nullHandler, nullProto], nullProto);
+
+// Proxy function with [[Call]]
+var callForCallOnly = function () { };
+callForCallOnly.toString = function() { return "callForCallOnly"; };
+var callOnlyHandler = { toString: function() { return "call-only handler"; } };
+testProxy("createFunction",
+          [callOnlyHandler, callForCallOnly], Function.prototype);
+
+// Proxy function with [[Call]] and [[Construct]]
+var callForCallConstruct = function() { };
+callForCallConstruct.toString = function() { return "call/construct call"; };
+var constructForCallConstruct = function() { };
+constructForCallConstruct.toString =
+  function() { return "call/construct construct"; };
+var handlerForCallConstruct =
+  { toString: function() { return "call/construct handler"; } };
+testProxy("createFunction",
+          [handlerForCallConstruct,
+           callForCallConstruct,
+           constructForCallConstruct],
+          Function.prototype);
+
+
+/******************************************************************************/
+
+if (typeof reportCompare === "function")
+  reportCompare(true, true);
+
+print("Tests complete");