Right now all of the WebRTC tests are mochitests, and steeplechase uses the same mochitest files for a special case. We should make steeplechase the default for all WebRTC tests which involve PeerConnection's. Executing steeplechase on one machine only should become the special case (e.g. for build machines).
The Sunny Day environment and the Platform Jenkins cross-platform instance will solve this when they are complete.
We know have at least a script in the steeplechase repository for running a steeplechase test locally with two instances of the same browser. So far only for Linux. But a first step to getting to this goal. Adding a script (or extend the existing script) to support Mac should not be too hard. No idea how to do accomplish this on Windows though.