I am using "Login with Google" and can't access stackoverflow from my account using Firefox. I tested this using 2 versions: At first I tried logging in using Firefox 21 Nightly, then I checked it using the Firefox 19.0.2 stable version (current). It told me that I am logged in with Google and have to refresh the page, so I click at the link and I am logged out. It works well at Chrome, but I would love to have this working with Firefox as well.
Although I could originally replicate this issue, I have just cleared all history from tools -> Clear Recent History menus.
It seems appears as though my firefox login is working correctly.