Are this chat using "long polling" or "http streaming" ?
It's not anything that simple. It uses http://www.mibbit.com/chat, which is a full IRC client written in Javascript and Java. Blog at http://blog.mibbit.com/.
Edit: Here's your answer.
The first part I got working was the communications between browser and server. That’s done using 2 XMLHttpRequests. The first one is simply to send data from browser to server. It utilizes keep-alive, to minimise new connections.
The second XHR is the ‘receive lazy polling’ one. It connects to the server, and the server holds it open until there are messages available, or a timeout expires. This one is also keep-alive, so the next request goes down the same connection.
What you end up with is 2 connections held open to the server, with packets (json in this case), and some http headers from time to time. To make sure the server would scale, I wrote a custom webserver in java using nio. It handles all of the connections in a single thread and as I say, scales to tens of thousands of connections.
If the client requests a new connection, it sends a request to the webserver, which then connects out, and starts proxying etc. It also runs an ident server in the case of irc connections so that an irc server can identify individual browsers. I looked at existing frameworks etc to do this sort of thing, but I valued learning how it all works, and thought that my use case may be specific enough to be able to optimise more than general frameworks can.