We've mentioned B2G before, but back then details were not easy to come by. For one, we were under the impression that the OS would be built on, or use parts of, Google Android. This is not the case; what B2G does make use of is Linux to handle the underlying hardware and "reduce the burden on ODMs/OEMs", according to Mozilla.
When I see stuff like this, I can understand why Microsoft went the direction it did with Metro. That said, B2G still needs to woo phone manufacturers before it can make any sort of retail impact, but with it sharing at least some compatibility with current Android phones, that doesn't feel like a massive barrier.