FirebaseUI authentication with Facebook not working

If you are using FirebaseUI, you must put this exact string in strings.xml:

<string name="facebook_application_id" translatable="false">APPID</string>

The APPID can be found on your developers.facebook.com dashboard.

See firebaseui-auth readme

Also be sure to add your android key hash and OAuth firebase URL in the facebook app.

this happened to me and might happened to some one , I forgot to enable facebook authentication in firebase console! goto firebase conosle and select your app then go to authentication->sign-in methods and enable facebook and add the app id and secret key from your facebook deevloper project

Try updating to the new release of Google Play services where they have fixed up some Firebase Authentication related issues. (Though they have not specifically mentioned regarding Facebook login)

Google Play services updated to 9.0.2 The Google Play services version 9.0.2 release is now available. This release fixes a known issue with Firebase Authentication where the FirebaseAuthApi is not available on some devices.

https://developers.google.com/android/guides/releases