The hidden directory created is .phoenix; I renamed it and tried to start again. Firefox gave the same error, and there was a new directory created in home called .phoenix. Reinstalling Firefox (via rpms) does nothing to fix this.
When it gives me this error, I've noticed that Firefox doesn't actually quit; ps -A | grep firefox shows:
4043 pts/1 00:00:01 firefox-bin
After killing firefox-bin and restarting Firefox, I get the same error again. Sigh.
(Konqueror still works (which is how I'm posting this), but when programs go boom for apparently no reason, it alarms me. Plus, Firefox owns Konqueror.) Any help appreciated!