What is Firebase? Is it Good or Bad?

Firebase is platform which allow to build web and mobile applications without server side programming language. You can store users data on its real-time database which sync data among users data in no time.

Pros:
=) JSON (Javascript Object Notation) storage means no barrier between data and objects
=) Simple serialization of app state
=) Minimal setup
=) Easy access to data, files, auth, and more
=) No server infrastructure needed to power apps with data
=) Massive storage size potential
=) Real time
=) Pretty much the most advanced hosted BaaS solution
=) Highly secure
=) Server less
=) Supported by Google!
Cons:
=) Not widely used or battle tested for Enterprises
=) Very limited querying and indexing
=) No aggregation
=) No map reduce
=) Can’t query or list users or stored files

Overall, If you doesn't know much about back-end technologies it's the best thing you can choose. Plus it gives first 50 connections (Means 50 users using the app at the same time) and 100MB storage for free. And even after that you only have to what according to your usage. Also it's really easy to use and handle.

But if you're looking to make a app with large photos and videos files then it can cost really high.

If you have more questions, put it in the comment section. I'll try my best to answer all your questions.