Well, it appears this crash is somewhat known by the Firefox developers, Bug 500105, but they haven't really found a reason that causes it. I'm going to ask you to run through a bunch of things just to see. Especially since you are having Bluescrrens in Windows, you are right this may be a hardware or Virus related issue.

Download and Install MalwareBytes Anti-Malware, run a full Scan. http://www.malwarebytes.org/

Download and Run TDSSKiller http://support.kaspersky.com/faq/?qid=208283363

Download and Install Microsoft Security Essentials http://windows.microsoft.com/en-US/windows/products/security-essentials (not an official endorsement, but I personally recommend MSE as an awesome permanent anti-virus)

Double check for all Windows Updates.

Update your graphics driver (Firefox uses your graphics card for some rendering, and an out of date graphics card driver can cause problems. https://support.mozilla.org/en-US/kb/how-do-i-upgrade-my-graphics-drivers.

Update all your plugins (Flash, Java, etc.): http://www.mozilla.org/plugincheck/.

After doing all these, run a chkdsk in Windows. Read http://support.microsoft.com/kb/315265, specifically the "How to run Chkdsk from My Computer or from Windows Explorer" Section. Make sure you check both boxes (this scan will take a long time probably).

After that, you can also run memtest. http://www.memtest.org/

If you are getting BSOD crashes they should take priority over Firefox problems. A web search should turn up memory testing applications, some of which will run independently of the OS. You may also need to consider the posiility of a malware problem. I would also look at video drivers, and consider using Windows own safe mode. Once your System is stable whilst using Windows XP you can investigate the firefox crashes.

See

• firefox crashes
• basic troubleshooting
• http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode
  no doubt there is a similar article on Windows XP
• http://en.wikipedia.org/wiki/Memory_tester and http://www.memtest.org/

Thanks for the answers, guys! I already checked for malware (via a bootable multi-engine antivirus dvd) but the system seems clean. I also made sure to have the latest drivers installed and checked my RAM with memtest. It turned out that one of the two RAMs was actually faulty so I got it out and it seemed to work fine for a while. Unfortunately the system just froze again (while FFox was running) with those strange artefacts on the screen. I'll have to check my VRAM and work through the rest of your suggestions now and report back if something FFox-relevant shows up. :(