I think a lot of members here have tried to use Firebase realtime database. This service is awesome, fast and has free tier.
Some apps can and will work nicely with Firebase (I love FirebaseDB component), but certainly not all apps are suitable to be paired with Firebase db.
I saw that sometimes some members here asking methods about how to do this or that with Firebase. Often the problems can be solved pretty easy with classic DBMS like MySQL. Sure sometimes you can force your way in hacky way with Firebase but it can come back with greater headache in later time.
What i propose to members that read this thread is please consider that Firebase database is not a potent medicine for all kind of apps…
This article here is a good read about this topic.