For anyone having the login problem, I've just experienced that problem today on Firefox 7 beta. Were you using Firefox beta or nightly?

I got the '400 error' in the Gmail Checker's debug log. Can you confirm this?

This problem however doesn't happen on Firefox 6 and before. Firefox must have changed something in the way it's making connections.

I'm really busy right now so I haven't got time to look into this thoroughly.