I managed to get a developer phone with Firefox OS at a dev conference. I can say that hands down it's the worst phone I've ever tried using. I used it as my primary phone for a week and the operating system made me avoid doing anything. Making a phone call was the most pleasant, but if I had to send a text or try and use one of the apps I just found myself locking the phone. The webapp as a phone app idea was just really unpleasant especially if you had limited connectivity.

I admire Mozilla for trying, but that OS would have taken a miracle to get it working in a good fashion.