I haven't looked at the code so I can't give you too much of a hard time (have you looked at it?) but the Firebase team might take issue with your use of the word 'slightly'.
I have looked at the code (and had looked at the code before leaving that comment). Please understand that the OT backend they are using is just something they got from someone else, so it isn't really interesting that the OT backend is open source. In essence, they just took an off-the-shelf open-source OT implementation and connected it to an off-the-shelf open-source HTML+JavaScript rich text editor.
The main thing that is difficult about building something similar to Firepad would be building the scalable distributed backend: there are no open source projects that I know of that provide that functionality. That is the value add of Firepad: the open source code is just some glue that you can find from other projects (including Etherpad, which is open source with both rich text and OT).
The thing that actually makes this interesting is the proprietary scalable synchronization backend from Firebase. That is interesting, no denial from me on that front: except for some issues with trusting the clients (pointed out in my other comment), this seems like a great and simple way for developers to rapidly get access to this collaborative text editing functionality for their applications. The open source parts, though, are not what is compelling.
To take some concrete examples: ShareJS is a strong implementation of OT (the guy is one of the people who had worked on Wave), but the backend they provide is less-than-stellar, based on fairly centralized storage into a small handful of backends, and no real attempt at supporting scalable front-end server endpoints (so, you have to have everyone connect to a single machine to act as the single-threaded mediator). Etherpad-lite is based on a similar architecture; you can shard these solutions on the document, but it just doesn't hold up in the same way Firebase does vertically.
Looking at this then from an alternative direction: one can imagine just taking the FirebaseAdapter from Firepad and wiring it into the backend of ShareJS. This isn't much work, and would probably be more useful than Firepad's current stack that is tied to the text editor: in addition to being able to use any of a number of text editors people have wired over ShareJS, ShareJS also supports arbitrary JSON document OT, allowing you to build systems that are closer in functionality to Wave (where people were using OT on the program state of things like chess games).
