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 Firefox with the the 
-profilemanager switch, e.g. firefox -profilemanager

If firefox doesn't start at all, first try and remove compreg.dat,
xpti.dat and extensions/Extensions.rdf in your profile-dir, or you
could just wack the old profile-dir,
    rm -r ~/.mozilla/firefox/<profile-dir> ~/.firefox/<profile-dir>
