If you're having difficulty signing in with Facebook, here are some known issues to help you troubleshoot:
1) Unconfirmed Facebook Account -- if you haven't 'confirmed' your Facebook account, logging into our site with Facebook Connect will not work. You must first confirm your Facebook account:
2) Browser Specific Issues -- in some cases, certain browsers mishandle the Facebook Connect login. In your Browser settings, ensure preferences → privacy → cookies and website is set to 'Allow from websites I visit'.