Despite of #17343 and #18959, these critical methods are still missing for the firebase_auth plugin.

FirebaseUser.updatePassword()
FirebaseUser.delete()

Due to security, updateEmail(), updatePassword() and delete() require a recent authentication, which then could be accomplished using the also absent FirebaseUser.reauthenticate().

Finally, without the one below, firebase e-mail templates will be sent only in English.
FirebaseAuth.setLanguageCode()