i'm curious about why did they go to "third"? there is a very big third Firefox OS not including WP. i can understand an OS based on Android. i can understand c

i'm curious about why did they go to "third"? there is a very big third Firefox OS not including WP. i can understand an OS based on Android. i can understand contributing to Firefox even forking. it has some real support from telecoms, open development process. apart from being a regional product which can get away with 3rd party app stores i dont get this write-a-mobile-os-from scratch.