After struggling a long time with implementing firebase to my android chat application. I finally made it work. With the power of Firebase database, your chat application is powerfull and seamless.
Only add the 'google-services.json' to your app for it to work.
Layout is simple, but it alligns itself to left/right, depending on the recipient/sender. The rest of the layout is lame, but that should be an easy fix for you.
Enjoy!