diff --git a/dom/base/MessagePort.cpp b/dom/base/MessagePort.cpp
index e2aa15457ae1..a7b593cad814 100644
--- a/dom/base/MessagePort.cpp
+++ b/dom/base/MessagePort.cpp
@@ -82,5 +82,25 @@ MessagePort::Entangle(MessagePort* aMessagePort)
   mEntangledPort = aMessagePort;
 }
 
+already_AddRefed<MessagePort>
+MessagePort::Clone(nsPIDOMWindow* aWindow)
+{
+  nsRefPtr<MessagePort> newPort = new MessagePort(aWindow);
+
+  // TODO Move all the events in the port message queue of original port to the
+  // port message queue of new port, if any, leaving the new port's port
+  // message queue in its initial disabled state.
+
+  if (mEntangledPort) {
+    nsRefPtr<MessagePort> port = mEntangledPort;
+    mEntangledPort = nullptr;
+
+    newPort->Entangle(port);
+    port->Entangle(newPort);
+  }
+
+  return newPort.forget();
+}
+
 } // namespace dom
 } // namespace mozilla
diff --git a/dom/base/MessagePort.h b/dom/base/MessagePort.h
index 5dab2db04589..84987c748f6a 100644
--- a/dom/base/MessagePort.h
+++ b/dom/base/MessagePort.h
@@ -49,6 +49,12 @@ public:
   void
   Entangle(MessagePort* aMessagePort);
 
+  // Duplicate this message port. This method is used by the Structured Clone
+  // Algorithm and makes the new MessagePort active with the entangled
+  // MessagePort of this object.
+  already_AddRefed<MessagePort>
+  Clone(nsPIDOMWindow* aWindow);
+
 private:
   nsRefPtr<MessagePort> mEntangledPort;
 };
diff --git a/dom/base/StructuredCloneTags.h b/dom/base/StructuredCloneTags.h
index aa3781b2a3e6..533d39f1b5e1 100644
--- a/dom/base/StructuredCloneTags.h
+++ b/dom/base/StructuredCloneTags.h
@@ -28,6 +28,7 @@ enum StructuredCloneTags {
 
   // These tags are used for both main thread and workers.
   SCTAG_DOM_IMAGEDATA,
+  SCTAG_DOM_MESSAGEPORT,
 
   SCTAG_DOM_MAX
 };
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 752389dfcb18..31480eba8f72 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -189,6 +189,8 @@
 #include "prenv.h"
 #include "prprf.h"
 
+#include "mozilla/dom/MessagePort.h"
+#include "mozilla/dom/MessagePortBinding.h"
 #include "mozilla/dom/indexedDB/IDBFactory.h"
 #include "mozilla/dom/quota/QuotaManager.h"
 
@@ -6750,6 +6752,7 @@ namespace {
 struct StructuredCloneInfo {
   PostMessageEvent* event;
   bool subsumes;
+  nsPIDOMWindow* window;
 };
 
 static JSObject*
@@ -6779,6 +6782,21 @@ PostMessageReadStructuredClone(JSContext* cx,
     }
   }
 
+  if (tag == SCTAG_DOM_MESSAGEPORT) {
+    NS_ASSERTION(!data, "Data should be empty");
+
+    MessagePort* port;
+    if (JS_ReadBytes(reader, &port, sizeof(port))) {
+      JS::Rooted<JSObject*> global(cx, JS::CurrentGlobalOrNull(cx));
+      if (global) {
+        JS::Rooted<JSObject*> obj(cx, port->WrapObject(cx, global));
+        if (JS_WrapObject(cx, obj.address())) {
+          return obj;
+        }
+      }
+    }
+  }
+
   const JSStructuredCloneCallbacks* runtimeCallbacks =
     js::GetContextStructuredCloneCallbacks(cx);
 
@@ -6819,6 +6837,16 @@ PostMessageWriteStructuredClone(JSContext* cx,
              scInfo->event->StoreISupports(supports);
   }
 
+  MessagePort* port = nullptr;
+  nsresult rv = UNWRAP_OBJECT(MessagePort, cx, obj, port);
+  if (NS_SUCCEEDED(rv) && scInfo->subsumes) {
+    nsRefPtr<MessagePort> newPort = port->Clone(scInfo->window);
+
+    return JS_WriteUint32Pair(writer, SCTAG_DOM_MESSAGEPORT, 0) &&
+           JS_WriteBytes(writer, &newPort, sizeof(newPort)) &&
+           scInfo->event->StoreISupports(newPort);
+  }
+
   const JSStructuredCloneCallbacks* runtimeCallbacks =
     js::GetContextStructuredCloneCallbacks(cx);
 
@@ -6910,6 +6938,7 @@ PostMessageEvent::Run()
   {
     StructuredCloneInfo scInfo;
     scInfo.event = this;
+    scInfo.window = targetWindow;
 
     if (!buffer.read(cx, messageData.address(), &kPostMessageCallbacks,
                      &scInfo)) {
@@ -7056,6 +7085,7 @@ nsGlobalWindow::PostMessageMoz(const JS::Value& aMessage,
   JSAutoStructuredCloneBuffer buffer;
   StructuredCloneInfo scInfo;
   scInfo.event = event;
+  scInfo.window = this;
 
   nsIPrincipal* principal = GetPrincipal();
   if (NS_FAILED(callerPrin->Subsumes(principal, &scInfo.subsumes)))
diff --git a/dom/base/test/Makefile.in b/dom/base/test/Makefile.in
index f6974304298c..1a8f9a00904b 100644
--- a/dom/base/test/Makefile.in
+++ b/dom/base/test/Makefile.in
@@ -32,6 +32,8 @@ MOCHITEST_FILES = \
   test_setting_opener.html \
   test_error.html \
   test_messageChannel.html \
+  test_messageChannel_cloning.html \
+  iframe_messageChannel_cloning.html \
   $(NULL)
 
 MOCHITEST_CHROME_FILES = \
diff --git a/dom/base/test/iframe_messageChannel_cloning.html b/dom/base/test/iframe_messageChannel_cloning.html
new file mode 100644
index 000000000000..ee53e855a730
--- /dev/null
+++ b/dom/base/test/iframe_messageChannel_cloning.html
@@ -0,0 +1,22 @@
+<!DOCTYPE HTML>
+<html>
+<body>
+  <script type="application/javascript">
+
+  function ok(a, msg) {
+    window.parent.postMessage({ status: a ? "OK" : "KO", message: msg }, "*");
+  }
+
+  window.addEventListener('message', receiveMessage, false);
+  function receiveMessage(evt) {
+    ok (evt.data, "Data received");
+    ok (evt.data.port instanceof MessagePort, "Data contains a MessagePort");
+
+    var a = new MessageChannel();
+    window.parent.postMessage({ status: "FINISH", port: a.port2 }, '*');
+  }
+
+  </script>
+</body>
+</html>
+
diff --git a/dom/base/test/test_messageChannel_cloning.html b/dom/base/test/test_messageChannel_cloning.html
new file mode 100644
index 000000000000..30327d5f1624
--- /dev/null
+++ b/dom/base/test/test_messageChannel_cloning.html
@@ -0,0 +1,70 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=677638
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 677638 - port cloning</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=677638">Mozilla Bug 677638</a>
+<div id="content"></div>
+<pre id="test">
+</pre>
+  <script type="application/javascript">
+
+  // This test checks if MessagePorts can be shared with iframes
+  function test_iframe() {
+    window.addEventListener('message', receiveMessage, false);
+    function receiveMessage(evt) {
+      if (evt.data.status == 'OK') {
+        ok(true, evt.data.message);
+      } else if (evt.data.status == 'KO') {
+        ok(false, evt.data.message);
+      } else if (evt.data.status == 'FINISH') {
+        ok (evt.data.port instanceof MessagePort, "Data contains a MessagePort");
+        window.removeEventListener('message', receiveMessage);
+        runTest();
+      } else {
+        ok(false, "Unknown message");
+      }
+    }
+
+    var a = new MessageChannel();
+    ok(a, "MessageChannel created");
+
+    var div = document.getElementById("content");
+    ok(div, "Parent exists");
+
+    var ifr = document.createElement("iframe");
+    ifr.addEventListener("load", iframeLoaded, false);
+    ifr.setAttribute('src', "iframe_messageChannel_cloning.html");
+    div.appendChild(ifr);
+
+    function iframeLoaded() {
+      ifr.contentWindow.postMessage({ port: a.port2 }, '*');
+    }
+  }
+
+  var tests = [
+    test_iframe
+  ];
+
+  function runTest() {
+    if (!tests.length) {
+      SimpleTest.finish();
+      return;
+    }
+
+    var test = tests.shift();
+    test();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTest();
+  </script>
+</body>
+</html>