new firebase with awesome features was just announced, but according to documentation (https://firebase.google.com/docs/android/setup#prerequisites) android studio (as well as gradle) is required now. For now in my cocos2d-x apps I have to use ADT/Eclipse to build apps, because gradle isn't supported yet (however cocos2d-x team is working on it). I'm now using an older version of the sdk, which is just a jar file. Is there a way to use new firebase in eclipse? What worries me the most is that plugin:
apply plugin: 'com.google.gms.google-services'
Take a look at this Github repository, I was using it as example to use Firebase with Eclipse (but finally I moved my project to Android Studio with Gradle because it was really awful).
README Project: https://github.com/dandar3/android-google-firebase-README
Actual Project: https://github.com/dandar3/android-google-firebase-common