So my boss downloaded the latest Firefox update. If you haven't seen it, it makes some dramatic changes to the look of Firefox. It also, for reason unknown, would not function properly on this crappy old computer at work. The screen would flicker, and then the computer would reboot. I uninstalled it and tried installing previous versions, however any new installation except for Firefox 2.0 has the same style and everything resulting in the same problem. I don't know if there's something in my registry that isn't being deleted or what, but it's a pretty big problem as many sites we use for work require Firefox 4.0 or higher, but even 4.0 has the terrible new setup that 9 does. Any ideas on what I can do to go to the version of Firefox directly before the latest update without it keeping those changes?

Alright, version 12. I dunno, I prefer not to update it if possible.

Computer uses Windows XP, presumably with all updates. Not sure how much RAM it has (not on that computer at the moment) but it's very much on the low end. There is more than ample free HD space. Yes I am an administrator. Have not downloaded Chrome, but IE does function properly, albeit extremely slowly which is why we use Firefox. Worth noting that trying to watch video on the computer has had a similar effect on the monitor which would make me think it was an issue with the video card, however it had never caused the computer to reboot before.

Won't be able to test until Wednesday when I'm at work again. 2.0 seems to be separate as well which is why it is no longer getting the crazy updated stuff from 12 that the other versions I tried see to have as well. However, it was running version 11 I guess? perfectly fine. There were no problems (except with streaming video) until version 12 and the stupid changes.