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
-profilemanager switch, e.g. mozilla -profilemanager

Or you could just delete the old profile-dir (note that this will delete
your saved bookmarks and settings):
    rm -r ~/.mozilla/default/<profile-dir>
