For one thing, Firefox on Android and Firefox OS arenconpletely different beasts, you can't really compare them. And the article here is about developer devices for FirefoxOS. :)
For the other, you probably tested the first variant of Firefox for Android that was available (which admittedly had a number of problems), while our mobile team has since rewritten Firefox for Android completely (well, not the web engine, but all the UI and Android logic) and that current variant is a completely different beast and praised by most that have tried it as the best browser for Android at this time. Give that current variant a try!
And, if you're not opposed to the idea that all mobile applications can be powered by HTML and JavaScript, then you surely should give FirefoxOS a try as well, maybe with one of those developer devices, once they're publicly available!