We are not saying to use Firebase although there is a firebase JS lib. If you use Chrome on Android it connects to FCM (which is backed by firebase product but

We are not saying to use Firebase although there is a firebase JS lib. If you use Chrome on Android it connects to FCM (which is backed by firebase product but it's not the same, it was called Google Cloud Messaging), if you Mozilla it connects to their push service. That's the way the spec works, the browser controls what push service you connect to.