Firebase auth with Facebook just stopped working on all our Polymer websites. One of them where updated 19th of march and has been working until yesterday/this afternoon (20
Graph API v2.2 has reached the end of its 2-year lifetime on 27 March, 2017, so this might be connected. You should check your library and possible updates. See this chart of deprecation dates, which lists v2.2 as available until March 25, 2017.
Firebase Authentication is having problems right now. Look at the Firebase Status Dashboard here:
https://status.firebase.google.com/