Thread drift....
The single biggest problem with Firefox is the profile has a habit of occasionally getting corrupted and the usual "solution" from the Mozilla crowd is to create a new profile
I can only warmly recommend the freeware "MozBackup". It saves and restores profiles and lets you chose what you want to restore, e.g. bookmarks only, additional stettings (like themes) or the complete profile. It also works well when you want to copy your profile to FF installations on other computers (just copy your saved profile and run MozBackup on the other computer). It might not work with FF 4 Beta though.