Funny, I've had exactly the same experience with the TS site as bellbram every time I've started up Firefox (same version). My privacy settings are pretty much identical... So it occurred to me that I hadn't taken a look at cache and cookies just now, and, voila! After dumping the old cookies, which were still there after the last upgrade to 2.0.0.6,
and the TS Site upgrade,
and clearing the cache, I just restarted the program several times and remained logged in.
Thanks for bringing it to my attention!
Chris K