Here are success stories of some Firebase Authentication integrations:
Fabulous implemented Firebase Authentication in one afternoon, making use of anonymous authentication, email and password based sign-in, Google Sign-in, and Facebook Login.
Rave (iOS, Android) was able to implement Firebase Authentication in one to two days on the client and in one hour on the server. This allowed Rave to quickly set up and run a multi-platform login system.
Kwaver Music: "The new version of Auth has allowed us to handle multiple social providers with ease! Linking accounts together has never been so simple." —James Zammit, VP of Engineering