Firefox OS and ZTE phone

Hi, I bought a ZTE phone with Firefox on it (from eBay for ca. $90, still on the way to me), mostly out of curiosity. I am browsing around about licensing and source code. Well, I find some information on the Mozilla website, with some hints about using Linux and some components. I have not find "the" source code yet. I am curious about it, how much of it is "vanilla Linux" and userland, how to get a shell, how to extend it, how to update etc. Do you know more about it? Regards Peter