In my Firefox ALL characters appear as squares filled with numbers. This includes text on any website, URLs in the location bar, the menus and dialogs and even the profile manager. I tried to fix it by reinstalling Firefox while removing my profile too (chosen from the uninstall dialog which works as normal). The first startup of Firefox works fine, from the second start on the characters are those squares again. All other Applications appear normal. How can I fix it? At the moment I cannot use Firefox at all.