A couple other users have reported the same issue this afternoon when trying to sign into that site with their Facebook accounts. I don't know whether this is a site issue or a Firefox issue. Logon problems are often related to cookies and cookie settings. Is this a new installation of Firefox with default settings, for example, you haven't disabled cookies or installed any privacy-related add-ons? You can double-check your cookie settings using the steps in this article: [[Websites say cookies are blocked - Unblock them]]. Also, could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: [[Troubleshoot Firefox issues using Safe Mode]]. ''If Firefox is not running:'' Hold down the Shift key when starting Firefox. ''If Firefox is running:'' You can restart Firefox in Safe Mode using either: * "3-bar" menu button > "?" button > Restart with Add-ons Disabled * Help menu > Restart with Add-ons Disabled and OK the restart. ''Both scenarios:'' A small dialog should appear. Click "Start in Safe Mode" (''not'' Refresh). Any improvement?