Some kind of bug with Facebook Connect is ruining the internet, picking people up and sending them to a useless error page. We can confirm that the bug is affecting numerous major sites, from Huffington Post and Salon, to our sister sites Polygon and SBNation, and even NBC News. If you’re being affected, it appears that logging out of Facebook remedies the situation. We’ve reached out to Facebook for comment, and will let you know as soon as we hear anything.
Update: That was quick. According to our developers, the issue has already been rectified. Facebook has also issued a statement, but it's choosing to keep quiet on exactly what went wrong.
“For a short period of time, there was a bug that redirected people logging in with Facebook from third party sites to Facebook.com. The issue was quickly resolved, and Login with Facebook is now working as usual.”