You could consider the Firefox reset feature, although that is easy to use it has a downside of removing some software extensions and settings you may have, but it will keep your passwords and bookmarks * see [[Reset Firefox – easily fix most problems]] The above article explains fully with pictures how to use the reset, for instance from the troubleshooting option, or the firefox safemode; and also lists what is and is not reset. If you are worried about what you could loose backup your profile first as that makes it easier to restore things to the way they were if necessary * see also [[Back up and restore information in Firefox profiles]] Put the copy of the profile somewhere safe and outside the Firefox paths, your Windows XP desktop is a suitable location for now. Post back with how you get on, although,you may then need to wait 6 weeks to confirm that you solved the problem fully.

I already tried that, didn't worked.