New Messenger for Firefox facility is down for a few hours. After user clicks on Turn ON, messenger sidebar opens but user can not Log In the system. So Facebook Messenger facility can not be used currently.
Please fix the issue if possible.
Go to Solution.
There is a bug about this and that Facebook is working on it.
(please do not comment in bug reports as that is considered as bug spam)
This has also been reported in this MozillaZine forum thread, so it looks that this is an issue with the Facebook site if it worked before.