Started on a project where I was using Webflow and Memberstack to develop an membership based application. Due to technical constraints with Webflow I made the decision to shift all my content over to Firebase. 

I want to keep Memberstack as my authentication and member management 

Can I link Memebrstack and Firebase? Seems Custom Auhentication would be the way to go. Anyone done this or know if this is possible? 
MemberStack gives you access to JWT tokens, and I use them in a screencast of mine walking through how to layer them on top of MemberStack for secure file downloads (e.g. each download link click authenticates before downloading).

You could certainly do the same to authenticate against your datastore in Firebase.

This should help you:

Awesome thanks for the speedy response Chris. I will take a look.