Originally Posted by machinist 
Uninstall FF completely then reinstall if you insist on using it
Not going to help at all. What you need to do is remove your FF profile, which resides in
C:\Documents and Settings\%username%\Application Data\Mozilla\Firefox\Profiles\%random folder name% - 'Application Data' is a hidden folder, so make sure you're showing all files.
Move the contents elsewhere on your hard drive, and FF will start a-fresh next time it loads. Import your
bookmarks.html file if you want to keep them.