How many concurrent AJAX (XmlHttpRequest) requests are allowed in popular browsers?

Question

In Firefox 3, the answer is 6 per domain: as soon as a 7th XmlHttpRequest (on any tab) to the same domain is fired, it is queued until one of the other 6 finish.

Wha

Answer 1

According to IE 9 – What’s Changed? on the HttpWatch blog, IE9 still has a 2 connection limit when over VPN.

Using a VPN Still Clobbers IE 9 Performance

We previously reported about the scaling back of the maximum number of concurrent connections in IE 8 when your PC uses a VPN connection. This happened even if the browser traffic didn’t go over that connection.

Unfortunately, IE 9 is affected by VPN connections in the same way: