Mozilla is taking the opposite approach. Their platform already has reasonable support because it doesn't take too much effort to port an existing web application to their platform. By making apps for their platform compatible with android, they might get developers building for Firefox OS first and then just reusing their Firefox app for android. It sounds like a bit of a stretch, but developers already do this with tech like phonegap. This will attract the same crowd as other html5->native app development platforms do.
The advantage for Mozilla here is that if developers use their devevelopers tools to make apps, their apps will look more in place on Firefox OS and advance the platform.