I'm finishing my app and It's still not published in Google Play. I already Generated Signed APKs and a keystore.jks for tests. But I lost the keystore. I made a new one and added it inside my firebase (because I use google auth).
Should I add the debug.keystore to firebase? And will there be any problems to release my app after creating a new keystore.jks?
Assuming your app isn't published, you don't need to worry. You can publish it using the new key.
Clean your project and rebuild it before you set the new key. Android Studio caches the previous path of the key so it may throw an error if you don't clean and rebuild.