And until today... its not much more than a lock screen, some webapps .. and some android ****

"Boot to Gecko (Firefox OS) uses a kernel derived from Android [...]"

"The first time you flash your phone, it must have Android 4 (Ice Cream Sandwich) installed. The process will not work correctly otherwise. Once you've done your first install of B2G, however, you can simply update on top of it."
(Source: https://developer.mozilla.org/en-US/..._mobile_device)