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I can not log into any Stack Exchange sites while using the Firefox nightly build built today (11.01.2013). When I try to log in, it just says welcome you have been logged in please refresh the page, and when I do that, it says you have been logged in redirecting and it just redirects infinitely.
I already tried deleting all cookies and clearing the cache.
This worked on nightly builds pre 10.12.2013.
What is the explanation?