As far as I know these APIs are not documented on MDN, although they are supported by Firefox (and Chrome, haven't tried in any other browsers). Spec: http://www.w3.org/TR/webmessaging/#channel-messaging.
The real spec is there: http://www.whatwg.org/specs/web-apps/current-work/#channel-messaging Also you find our implementation info here: http://mxr.mozilla.org/mozilla-central/source/dom/webidl/MessagePort.webidl (Although it should implement the Transferable helper methods, it doesn't) and http://mxr.mozilla.org/mozilla-central/source/dom/webidl/MessageChannel.webidl As it will supported in Workers, we need to be sure to update this page, if needed: https://developer.mozilla.org/en-US/docs/Web/API/Worker/Functions_and_classes_available_to_workers Relevant implementation bugs I found (useful for compat data): bug 677638 (initial implementation in Fx 26, preffed off by default), major fix in Fx 31 (bug 912456). For workers: bug 911972. (not yet landed) Note that this API is still off by default: bug 952139 is about activating it.
Chris did it.