When I had my PC on for 3 1/2 days straight while I was at my grandmas I was scared it was gonna burn down my house, and/or get stolen ;_;
I was hosting a minecraft server, and every few hours I would log into it to reassure myself everything was fine. True story.
Idkbutlike2, reinstall firefox. If there's anything you want to keep, use a program called MozBackup to back everything up. Reinstall, see if it's still an issue. If it goes away, use the backup thing to restore it, and if it comes back you can identify the problem.
yeah I'm just saying that coz I'm not having the problem lol.
problem is that even if your einstall firefox the problem will remain because windows likes keeping saved data or something you'd have to figure out how to completely delete everything affiliated with firefox. I'd suggest you google for that
I just turn off my compute before I go to sleep, unless I'm torrenting or something like that. If the computer isn't doing anything, no point in keeping it on while I sleep.