If you encounter strange problems relating to bookmarks, downloads,
window placement, toolbars, history, or other settings, it is
recommended that you try creating a new profile and attempting to
reproduce the problem before filing bugs.
In order to create a new profile, start Mozilla with the the 
-profilemanager switch, e.g. mozilla -profilemanager
   
Or you could just wack the old profile-dir,
    rm -r ~/.mozilla/default/<profile-dir>