I’m using many of the services Google has to offer, GMail being one of the many. I’ve noticed a couple of times now that when I logout from Google’s single-sign-on, but then go back to GMail (type in URL, not back-button) I’m still logged in despite that the Google main page or any of the other services. I can even access all sorts of old email so it’s not some strange cache-issue. I can’t quite reliably reproduce it, but it happens somewhat frequently.
I’m wondering whether Firefox does something strange in the way it clears cookies or does Google use an extra authentication-cookie for GMail that is not always deleted.