In Internet Explorer 8 and Firefox 3, the maximum number of concurrent connections from a single host has changed. Unfortunately, this will sometimes cause problems with a web server, so it may be in your best interest to limit the number of concurrent connections to the two (2) allowed by the HTTP/1.1 specification.
When this page loads it should queue ten (10) AJAX sessions, each one getting a different page from this site. If you are using Firebug when loading this page, you will be able to see the log message in the console demonstrating that each connection is closed before the next connection is opened.