Make sure your emulator has the Play Store.
When you do not have Play Store installed on the emulator, this error occurs.
This issue happened to me after changing the firebase rules. My IOS Simulator worked just fine but Android Emu did not. I fix this by wiping all data from my device in my emulator and then re-launching the EMU. Probably you dont even need to wipe data from emulated device.
Try re sync your client with your Firebase app, and add again the .json file. In android studio 2.3 just click on tools>firebase and in the assistant check if your app is connected to.
Check in your Firebase console that "anonymous auth" is allowed. It should solve your problem.
Also check INTERNET permission in your manifest. It so obvious, but...
Good Luck.
Log into your firebase console and Enable Email/Password Sign-In_Method, it should solve the issue.
Make sure you have to tack care of
Internet Permission ,compile library and Enable only one Auth From firebase auth list not.
In my case i enable 2 Authentication from list Google and Email/Password, so that is not work but after disable Google.. then its work correctly.
I hope my answer is help you.