Compared to the typical firefox release it has many new features indeed. In my opinion the most important by far is H.264 support. With that feature and an addon to change the user agent on a per website basis I can have flash disabled most of the time at last. I hope the guys at mozilla bring this support on all os soon.
By the way, I don't know why these guys are investing time in supporting ARMv6 when firefox is obviously a resource hungry browser. Minimum RAM required is 384 MB so I don't think there will be many ARMv6 devices out there that can use firefox.
In the initial FFOS devices they will be running on arm A5. Although they are using v7, they are only a bit faster than the old arm 11.