Don't know which upgrade made this change, but if you had clear cache when Firefox exits set, the rules have changed and now Firefox exiting also clears cookies. You need to unselect cookies by performing: Tools -> Options -> Privacy, then select 'use custom settings for history; check 'clear history when Firefox closes; click the settings button; uncheck clear cookies. I also suggest ONLY checking off 'cache' from the options (i.e. uncheck all other options). Hope this helps someone with this issue.