As for the adoption of a FB browser, I would be curious to see how it would fare. I'm pretty convinced that most early adopters which sustained the initial adoption of Firefox and Chrome would never use a FB browser, because they would be worried about Facebook becoming the sole owner of the internet - and because they're perfectly able to be always on on FB, should they want to.
Could the typical Facebook user become an early adopter? Everything's possible, but it wouldn't be very easy.