Firebase gives you a real-time database with no initial setup. The only really big competitor I know of it is RethinkDB. Having "three-way" databinding in a SPA is pretty cool and wouldn't be something that would be trivial to setup without either of these two databases.
I could see Firebase being a great go to for a certain size of project in the small to medium size that would rather pay for this feature set that using AWS, Azure, Rackspace, etc.
I could see Firebase being a great go to for a certain size of project in the small to medium size that would rather pay for this feature set that using AWS, Azure, Rackspace, etc.