What's interesting for us is that it's heavily based on android. Basically they've kept the HAL, hacked out Dalvik and anything java, and replaced it with Gecko. In theory any device that runs Android can run FirefoxOS.
It's still alpha software, it's supposed to eventually be compatible with ARMv6 devices, but as I found out while trying to build it for my LG Optimus One, Gecko is still hardcoded in many places to ARMv7. Their test devices include the Galaxy Nexus and Galaxy SII, so special hardware isn't needed.
Therefore it should run fine on the Nexus 7 right?
Well, not quite. FirefoxOS is based on ICS, but Nexus 7 runs only Jellybean.
I've tried building with ICS sources and Jellybean sources, making the necessary changes to get it to build. However with Jellybean sources it doesn't get past the Google screen, and ADB loops without many error messages to analyse. With ICS sources ADB isn't even accessible, the kernel and/or the proprietary blobs are probably not compatible.
If anyone wants to take a look at my changes, they're at my github. Some of the changes to Gecko I got from this bug at Mozilla, but it's out of date and incomplete (there is a patch in the B2G repo).
Hopefully with more eyes looking at it, we'll get it working!