Are you clearing cookies as Firefox is shut down?
Some 'security' applications mess with Firefox and do the clearing automatically, so you may need to check the setting in that application to see if if is enabled.

There are 'special' cookies that retain the the "remember me function that a web site will send to Firefox when the user has that feature selected on the web site's server.

I delete cookies thru IO once a white, but it hadn't happen like this before.

I had this problem, too. I ran the "free up disk space" utility under the Security options in Control Panel and it fixed it (although I still have to sign in at the start of a new boot-up session). I'm guessing that some cookie or file in Firefox was corrupted and this cleaned it out.