From Firefox 3 RC2, when I logged out of Hotmail (it couldn't successfully log me out of C9 btw); and when I attempted to go to the C9 main website, it went into a loop of "Please sign in" prompts.

I can reproduce, and so can you if you're on that browser, haven't tested with IE.

In the meantime, I will sign in with my C9 account so that I dont have to use a Live ID and go through this bug again.