Comment 55 for bug 305394

> However if I start FF3.5 or TB3 with gksudo

oh. please dont do that. besides from general security hazards, doing this calls for troubles and usually does not help (except for cases where you already ran them as root before!!); running this as root creates files/caches as root in some system directories and that might also cause issues lateron, when the user cannot recreate/invalidate those.

> .fontconfig

usually font config caches work quite well, i would think that you had a manually setup (and most likely broken):

> .fonts.conf