Why would FireFox cause a Classic ASP + ASPNET MVC 2 site to consume max RAM and CPU on a server?

I recently inherited a dinosaur Classic ASP site that has some fresh blood pumped in to it in the form of intertwined ASPNET MVC 2. I have duplicated the site on the same server (Windows 2008 R2, 4GB, quad core, VM) to set up a poor man's staging site.

As we were trying to sort some legacy bugs in the Classic ASP admin module, we noticed that the RAM usage would steadily go up from about 1.3GB (including system usage and 3 other sites) to max out at 4GB over the course of about 3.5 minutes. The CPU usage would get close to max on all cores, but only when we tested with FireFox (latest 3.6.9 and 3.6.8 - we didn't have older versions lying around to test with).

We tested the same pages 开发者_运维问答with IE8, IE7 via compatibility mode, IE6 with IETester, IE7 with IETester, latest Chrome, latest Opera and latest Safari, but all would behave normally. The live version of the site does not have this issue. FireFox runs very well, almost as well as Chrome, and much better than all versions of IE.

Has anybody come across anything like this before? Any ideas on hunting down the issue? I could probably nuke the staging site and try to set it up from scratch but I am intrigued as to how a particular browser could cause a server issue.

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We experienced the same thing with a classic ASP site and FireFox 3.6.*.

We profiled the code heavily and found nothing unusual.

The problem disappeared when Fireforx updated.

Weird!

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We found that the issue fixed itself by FireFox updating itself over the course of a few weeks. One of the oddest bugs I have come across and little chance of finding an answer now.

@Andrew Barber - I used Fiddler and there didn't seem to be anything that stood out in the data being sent/received between the diff browsers. Thanks for the tip though, was handy in helping rule out a few more things.

Cheers