Load Firefox Safe-Mode.

In Start > All Programs > {the folder where Mozilla Firefox is}, select "Mozilla Firefox (Safe Mode)".

If FF loads correctly, see if you can save your Bookmarks. Bookmarks > Organize bookmarks > Import and Backup, then export to HTML.

If FF Safe Mode fails to load, then it seems your only course is to uninstall. If you are using Windows, perhaps System Restore can help there.