Is it possible to have a presence mechanism work for hundreds to potenailly thousands of firebase "friends"?

Question

I'm building a chat app for a social network. Each user can have lots of friends. I'm trying to figure out the most efficient way to build a presence detection system for a chat app. Is this a scaling problem that will kill an app? Imagine the network having hundreds of thousands of users. A user has hundreds of friends and wants to sense when any of them are online when they have their chat app up. Is this possible? If so, is there a recommended efficient way to do this?