That's a good question, and I don't have an answer for you. However, since I've heard how awesome Firebase is, I'm wondering what you offer over Etherpad. After Google acquired it and open sourced the engine, lots of other websites have sprung up that use it. I'm sure there are great reasons to use your tool rather than an Etherpad-based one, so it'd be interesting to hear them!
The main reason you might want to use Firepad instead of Etherpad is if you don't want to run the server-side piece of Etherpad. For example, if you're stack is different than theirs it might be a pain to set up a special server environment just for the collaboration portion of your app.
Firepad is fully client-side code, so there's no server software for you to set up.
The other big reason you might use Firepad is to get all of the other goodies that Firebase provides, like the automatic scaling, Forge debugger, declarative security, etc.
So, when you say it's "fully client-side code" -- what that looks to me to mean is not that it's not talking to a server somewhere, but that it's talking to Firebase's servers rather than my servers. Is that correct?
Most every Etherpad implementation I've seen is pretty much a direct copy of what Etherpad was. I have no idea if this is inherent to the Etherpad source, but it sure seems it. The entire point of Firepad is that you can use it for much more custom use cases, like Socrates: http://socrates.io — no crappy word processing UI, or any of that stuff. Totally custom and easy to do.
http://etherpad.org/
http://piratepad.net/
http://titanpad.com/
http://www.cynapse.com/syncin
http://openetherpad.org/
Mozilla and no doubt many others can easily deploy it on their servers:
https://etherpad.mozilla.org/