It's not like every Firefox extension will be broken. And I'm an ex Firefox user who switched to Chrome for the sandboxing and multiproc architecture. I'll happy go back to Firefox, I'd much rather use a browser by Mozilla over Google.

Maybe in the short term keeping some users is worthwhile but they'll continue to lose them slowly to Chrome, and browsers aren't fighting a short game. Firefox, Chrome, IE, they're not going anywhere - they've been around for a long time with plenty of market share. It makes sense to be forward thinking here.