diff -r 000000000000 -r 6474c204b198 toolkit/components/social/MessagePortWorker.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/social/MessagePortWorker.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,110 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// Note: this is never instantiated in chrome - the source is sent across
+// to the worker and it is evaluated there and created in response to a
+// port-create message we send.
+function WorkerPort(portid) {
+  AbstractPort.call(this, portid);
+}
+
+WorkerPort.prototype = {
+  __proto__: AbstractPort.prototype,
+  _portType: "worker",
+
+  _dopost: function fw_WorkerPort_dopost(data) {
+    // postMessage is injected into the sandbox.
+    _postMessage(data, "*");
+  },
+
+  _onerror: function fw_WorkerPort_onerror(err) {
+    // We throw an object that "derives" from the exception, but with
+    // a more detailed message.
+    throw {message: "Port " + this + " handler failed: " + err.message, __proto__: err};
+  }
+}
+
+function importScripts() {
+  for (var i=0; i < arguments.length; i++) {
+    // load the url *synchronously*
+    var scriptURL = arguments[i];
+    var xhr = new XMLHttpRequest();
+    xhr.open('GET', scriptURL, false);
+    xhr.onreadystatechange = function(aEvt) {
+      if (xhr.readyState == 4) {
+        if (xhr.status == 200 || xhr.status == 0) {
+          _evalInSandbox(xhr.responseText, scriptURL);
+        }
+        else {
+          throw new Error("Unable to importScripts ["+scriptURL+"], status " + xhr.status)
+        }
+      }
+    };
+    xhr.send(null);
+  }
+}
+
+// This function is magically injected into the sandbox and used there.
+// Thus, it is only ever dealing with "worker" ports.
+function __initWorkerMessageHandler() {
+
+  let ports = {}; // all "worker" ports currently alive, keyed by ID.
+
+  function messageHandler(event) {
+    // We will ignore all messages destined for otherType.
+    let data = event.data;
+    let portid = data.portId;
+    let port;
+    if (!data.portFromType || data.portFromType === "worker") {
+      // this is a message posted by ourself so ignore it.
+      return;
+    }
+    switch (data.portTopic) {
+      case "port-create":
+        // a new port was created on the "client" side - create a new worker
+        // port and store it in the map
+        port = new WorkerPort(portid);
+        ports[portid] = port;
+        // and call the "onconnect" handler.
+        try {
+          onconnect({ports: [port]});
+        } catch(e) {
+          // we have a bad worker and cannot continue, we need to signal
+          // an error
+          port._postControlMessage("port-connection-error", JSON.stringify(e.toString()));
+          throw e;
+        }
+        break;
+
+      case "port-close":
+        // the client side of the port was closed, so close this side too.
+        port = ports[portid];
+        if (!port) {
+          // port already closed (which will happen when we call port.close()
+          // below - the client side will send us this message but we've
+          // already closed it.)
+          return;
+        }
+        delete ports[portid];
+        port.close();
+        break;
+
+      case "port-message":
+        // the client posted a message to this worker port.
+        port = ports[portid];
+        if (!port) {
+          // port must be closed - this shouldn't happen!
+          return;
+        }
+        port._onmessage(data.data);
+        break;
+
+      default:
+        break;
+    }
+  }
+  // addEventListener is injected into the sandbox.
+  _addEventListener('message', messageHandler);
+}
+__initWorkerMessageHandler();