diff -r 000000000000 -r 6474c204b198 toolkit/components/social/MessagePortBase.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/social/MessagePortBase.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,108 @@
+/* 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/. */
+
+// Code that is shared between clients and workers.
+this.EXPORTED_SYMBOLS = ["AbstractPort"];
+
+this.AbstractPort = function AbstractPort(portid) {
+  this._portid = portid;
+  this._handler = undefined;
+  this._closed = false;
+  // pending messages sent to this port before it has a message handler.
+  this._pendingMessagesIncoming = [];
+};
+
+AbstractPort.prototype = {
+  _portType: null, // set by a subclass.
+  // abstract methods to be overridden.
+  _dopost: function fw_AbstractPort_dopost(data) {
+    throw new Error("not implemented");
+  },
+  _onerror: function fw_AbstractPort_onerror(err) {
+    throw new Error("not implemented");
+  },
+
+  // and concrete methods shared by client and workers.
+  toString: function fw_AbstractPort_toString() {
+    return "MessagePort(portType='" + this._portType + "', portId="
+           + this._portid + (this._closed ? ", closed=true" : "") + ")";
+  },
+  _JSONParse: function fw_AbstractPort_JSONParse(data) JSON.parse(data),
+
+ _postControlMessage: function fw_AbstractPort_postControlMessage(topic, data) {
+    let postData = {
+      portTopic: topic,
+      portId: this._portid,
+      portFromType: this._portType,
+      data: data
+    };
+    this._dopost(postData);
+  },
+
+  _onmessage: function fw_AbstractPort_onmessage(data) {
+    // See comments in postMessage below - we work around a cloning
+    // issue by using JSON for these messages.
+    // Further, we allow the workers to override exactly how the JSON parsing
+    // is done - we try and do such parsing in the client window so things
+    // like prototype overrides on Array work as expected.
+    if (!this._handler) {
+      this._pendingMessagesIncoming.push(data);
+    } else {
+      data = this._JSONParse(data);
+      try {
+        this._handler({
+          data: data,
+          __exposedProps__: {
+            data: 'r'
+          }
+        });
+      } catch (ex) {
+        this._onerror(ex);
+      }
+    }
+  },
+
+  set onmessage(handler) { // property setter for onmessage
+    this._handler = handler;
+    while (this._pendingMessagesIncoming.length) {
+      this._onmessage(this._pendingMessagesIncoming.shift());
+    }
+  },
+  get onmessage() {
+    return this._handler;
+  },
+
+  /**
+   * postMessage
+   *
+   * Send data to the onmessage handler on the other end of the port.  The
+   * data object should have a topic property.
+   *
+   * @param {jsobj} data
+   */
+  postMessage: function fw_AbstractPort_postMessage(data) {
+    if (this._closed) {
+      throw new Error("port is closed");
+    }
+    // There seems to be an issue with passing objects directly and letting
+    // the structured clone thing work - we sometimes get:
+    // [Exception... "The object could not be cloned."  code: "25" nsresult: "0x80530019 (DataCloneError)"]
+    // The best guess is that this happens when funky things have been added to the prototypes.
+    // It doesn't happen for our "control" messages, only in messages from
+    // content - so we explicitly use JSON on these messages as that avoids
+    // the problem.
+    this._postControlMessage("port-message", JSON.stringify(data));
+  },
+
+  close: function fw_AbstractPort_close() {
+    if (this._closed) {
+      return; // already closed.
+    }
+    this._postControlMessage("port-close");
+    // and clean myself up.
+    this._handler = null;
+    this._pendingMessagesIncoming = [];
+    this._closed = true;
+  }
+};