I was getting this weird error on my google developer console. So i used google Cloud Test Lab to See whats really happening. turns out my app is failing on almost all devic
If this can help other I solved this using this, although this is nowhere linked with Firebase but it actually solved my crash
Add compile 'com.android.support:multidex:1.0.1' to app/build.gradle.
Add android:name="android.support.multidex.MultiDexApplication" to the application tag in AndroidManifest.xml.
If you are using a custom Application class, skip the AndroidManifest.xml and make your Application class extend MultiDexApplication instead of Application.