Um... Blackberry? That's an alternative to iOS and Android. And hey, it's already available, super stable, and feature rich! I like my Bold 9900 with OS7. The *only* thing I don't like is the slow shutter speed on the camera, that has more to do with me being too cheap to buy a real camera than it does a smart phone not performing like a real camera.
Anyhow, I don't see Firefox OS and Ubuntu phones doing any better than WebOS or Windows phones. WebOS was better than Symbian, yet Symbian and Blackberry ruled until iOS won the mind share. Then Android stole the show, but Symbian, Blackberry, and iOS are all still out there on millions of devices. Sadly, Windows Mobile/7/8 has always been a joke.