In terms of usage and leverage, it doesn't seem to be moving a needle. It's been around for quite awhile and still has an awfully small market share.

That said, Firefox for Android is a great technical accomplishment, and a valuable project. The fact that they are able to differentiate themselves with extensions is very powerful.

The fact that this awesome accomplishment hasn't made much impact in share probably proves that "customization" isn't going to significantly outweigh "default" in that market, though my guess is it would still be a leading factor for the very small number of people who aren't using the default browser.

I don't mean to say that Mozilla should avoid mobile efforts entirely. Fennec is necessary, and I think Firefox OS would have been a fantastic reference implementation if Mozilla hadn't chased partnerships and commercial releases in combination with it.

The problem wasn't that Mozilla put time or resources into these things, it was that Mozilla bet on these things to the detriment of their core competencies and, frankly, mission.