I really wish Mozilla would put the resources currently behind Firefox OS and use them for something like a modern libgecko and standalone gecko wrapper that runs on different environments instead of making an OS.
The blink/webkit monoculture is causing issues but every app is embedding it because gecko as a platform for embedding is essentially dead.
At this point making gecko nicely embeddable is not worth the cost in engineering resources compared to what it would bring in. Servo, the next generation browser is being designed to be easy to reuse and this is what Mozilla is focusing on in this area.
If I had a dollar for every time I saw the argument "I wish Mozilla would put resources into <project I like>, and stop wasting money on <project I don't like>"... I would have a big pile of dollars.
I think it is unlikely that the presence of a nice libgecko would change the dominance of Blink/WebKit on Android and iOS. Mozilla didn't really enter that fight, but even if we had I think we'd have lost (which frankly makes our lack of effort there seem wise).
The blink/webkit monoculture is causing issues but every app is embedding it because gecko as a platform for embedding is essentially dead.