r2d2b2g is an addon, but it bundles B2G Desktop nightly builds, which are native executables, and thus the addon is platform-specific, with packages available for Mac, Linux 32-bit, and Windows (caveat: B2G Desktop for Windows currently crashes on startup due to bug
The packages are large, 50-60MB each, partly because of the executables, but mostly because they also bundle Gaia profiles, including all default apps. (It's probably worth bundling a few of these, for demonstration purposes, but we could make the packages much smaller by removing the rest.)
r2d2b2g uses the Add-on SDK as its addon framework and relies on several third-party addon modules (subprocess, menuitems) along with some Python utilities (mozdownload, mozbase) to download and unpack B2G Desktop builds. Plus Gaia, although recent work to bundle Gaia profiles with B2G Desktop builds may break that dependency.
I've demoed the project to a variety of folks over the last couple weeks, and I've received a bunch of positive feedback about it. B2G Desktop combines approachability with phoneliness and is the best existing test environment for Firefox OS. But its configuration is a challenge, and it provides no obvious affordances for installing and testing your own app. r2d2b2g shows that these problems are tractable (even if it doesn't yet solve them all) and demonstrates a promising product path.
After seeing r2d2b2g, Kevin Dangoor drafted a PRD for a Firefox OS Simulator that I'll use to guide further development. Interested in participating? Clone the code from its GitHub repository and contribute your improvements!