Mozilla already supports (in code, not principle) H.264 by leveraging non-Mozilla code. It's not usually a problem on Windows on Mac since the user has already paid for a license when they bought the OS, but on Linux (gstreamer) it can cause patent violations within US.
I hope (an believe) Mozilla will keep that functionality to use one of multiple backends (Windows's fedia framework, gstreamer etc.) when it adds this Cisco binary.
We will need WMF at least until OpenH264 does High Profile, and I believe we are not going to be able to use only the OpenH264 binary blobs. Therefore we'll support other back ends (but not necessarily all possible back ends).
I hope (an believe) Mozilla will keep that functionality to use one of multiple backends (Windows's fedia framework, gstreamer etc.) when it adds this Cisco binary.