Sounds like your profile is corrupt...

2 things you can do, first save your bookmarks to a location like my documents, then either clear out all of your cookies and cache with Crap Cleaner that may do the trick, or as a last result, completely uninstall FF, go to files and delete folders called Mozilla and Firefox, reboot and install a fresh version of Firefox, and import your saved bookmarks.


Profiles Mozilla FAQ

Some more Tips

Luck...