We are about to switch to Firebase notifiaction API from Parse.com (that are retiring their service in jan 2017) to send push notification to our android and iOS Apps.
When you send notifications from the Firebase Notifications console, you get statistics about how many people received and opened the messages. But there is no API (yet) for Firebase Notifications.
If you're using the Firebase Cloud Messaging API (https://fcm.googleapis.com/fcm/send), the message statistics don't show up in the Firebase Notifications console. You can (as AL. says) get delivery statistics in the Google Play Developer Console in that case.