We are currently struggling with firebase messaging in a multi million user android app. Receiving lots of quota errors which are preventing push notifications to work properly. There is contact support with the firebase team, but there is no solution. I learned that the firebase infrastructure is shared with other developers. If one developer is maximizing load on the system it affects others. The fact that you basically have no alternative to firebase fcm is really a pita. Each new version of Android makes it more restrictive. I wouldn't be surprised if in 2 years from now every app needs to have buttons with a predefined colour and fontsize