don't.
the work so far can all be done with emulator. DO NOT BUY A DEVICE. and as the parent just said, the performance on the emulator is MUCH better than the real device.
it is just more waste in the world.
Also, if anyone want a couple firefox phones msg me. i have a couple left. i got them when i believed that since they were going to be sold in stores, they would be consumer ready... and hence i needed to support them on my site... big mistake on all accounts. to being with they are not consumer ready. and it was close to impossible to find them in stores (despite them being advertised on billboards all over the city)
anyway, if you want a phone, msg me. i have a few left. be warned that is harder to flash than a re-purposed android phone. much. much harder. (extremely closed components and hard to crate kernels)
This is not hate on the project. just on their careless aggressiveness to go to market. the project has lots of future. just take your time before polluting the world with pure garbage.