You need to fix the "hangup" issue that firefox has. I close the browser, and 24 hrs later, it's STILL eating up all my processor time.. this IS an issue you need to have fixed.
I dual boot between Win XP Pro x64 and Win 7 Ultimate x64. I also have a 2nd pc running strictly XP Pro 32 bit, and it's the same problem. Close the browser, and everything else takes a long time to load, even the security screen for Win7. then it takes a few minutes for task manager to show up. Seriously, I love the browser any day of the week over Chrome or IE. Fix it. kinda hard to do much when the browser is eating 90%+ of the processor
Opaite Mbohovái (3)
Sometimes an external program or Firefox extension or plugin causes the Firefox process to "hang" and not close properly. See the hang-at-exit section of this support article.
https://support.mozilla.com/en-US/kb/Firefox%20hangs
I only have 32 bit XP systems and the nearest I get to dual booting is having the XP Recovery Console available as a boot option.
I certainly do not see firefox using excessive processor time; without good reason; even on my legacy machines, and it does not continue after it is shut down. Sorry that my answer is not helpful, but I am wondering if problems may be specific to your own systems, or what you are doing, rather than to firefox in general.
I greatly appreciate the suggestions and the links.. I honestly looked earlier, but didn't find the ones you posted. My fault there. I have looked at them, and for all intents and purposes, I've already taken the steps they've suggested: disabled all plugins and extensions. Removed/uninstalled all plugins/extensions. Uninstalled and re-installed Firefox, no plugins or extensions. The problem still occurs. This isn't a problem that just started occurring, but has been relatively consistent in appearing since, v3.1 ( i think? Been going on for quite awhile)
I'll continue to try and find just what is happening, but honestly.. I really do not believe the problem is my system.