One possible reason for this is if Firefox believes that it crashed during the last shutdown. It will try to resume your previous session after any crash. (This can be changed if necessary using hidden settings.) Another possible reason is a user.js file which contains a preference to resume your previous session once, overriding your normal setting. This article describes how to check for that possibility: [[How to fix preferences that won't save]]. Could you check that out and report back on whether you find anything? Note: If you find a file named user but not user.js, Windows may be hiding file extensions from you. To work with files as accurately as possible, I suggest unhiding them. This Microsoft support article has the steps: [http://support.microsoft.com/kb/865219].

Thank you for your prompt help. Thanks