I found this information in a search and like it's worth a try.
i would try deleting the hidden mozilla configuration files....first back up your favorites/bookmarks
next, open your home folder and in the toolbar, click "view"...then put a check next to "show hidden files"
find the .mozilla folder, right click on it and choose "move to trash"
try to open Firefox again and see if it works.
This looked like the most workable solution from all of the search results I found. Firefox will recreate the deleted file when it starts. Lets keep our fingers crossed on this one.