Right now I'm exploring how to write an API using Express and MongoDB. I'm also using Angular to do my routes and views. I know Firebase and AngularFire can make it so I can bypass using Express all together (or so I think) and have my app be realtime.
In this article by Chris Esplin he states that he could not give up Express because he needed it to write promises instead of callbacks for cleaner code when using his npm package 'Quiver-Invoice' with Firebase, Stripe and MailChimp's Mandrill service.
In this SO post the poster says they need to use Express & Node for the ability to send emails out. I assume this is impossible if one uses only Firebase with Angular.
Also I have seen people talk about differences in authentication and security differences between the two here https://groups.google.com/forum/#!topic/firebase-talk/WF9gf--A3Qo
Question(s)
So what are the core differences between Firebase and Express?
Is it possible to build an API around Firebase like I can do in Express + MongoDB?
Is it possible (or will it be possible soon) to customize the Firebase server like one can with Express?