There is also an experimental technology called Broadcast Channel API that is designed specifically for communication between different browser contexts with same origin. You can post messages to and recieve messages from another browser context without having a reference to it:
var channel = new BroadcastChannel("foo");
channel.onmessage = function( e ) {
// Process messages from other contexts.
};
// Send message to other listening contexts.
channel.postMessage({ value: 42, type: "bar"});
Obviously this is experiental technology and is not supported accross all browsers yet.
