Firebase : How To Paginate - A Quick Guide
Pagination, or “How to Fetch a Data Set in Parts” You want to provide a quick initial set of data to your Firebase user, say the first 5 blog posts. If they want more, you can serve up what is needed, always being considerate of their waiting time and network data usage.
This is a great design pattern, because it is optimising the right thing at the right time. At the start, you care most about speed, and giving the user something to work with.