I haven't used Firefox on Android in quite a few months but last I checked I hated the rendering performance compared to Opera Classic or Chrome. I would double tap or zoom in and it would still take a second or two to render that zoomed-in image. It was quite frustrating. Granted, it happened on a lower-end phone then, but wouldn't happen on the other browsers.

Firefox with Servo looks fantastic, though, and from their roadmap it seems Servo will be coming to mobile first, this year. I'm really hoping for a multi-process highly parallel completely rewritten in Rust Firefox within the next two years.

http://www.phoronix.com/scan.php?page=news_item&px=MTgzNDA