A:
Windows RT only runs programs installed through the Windows Store. While Mozilla or Google COULD develop browsers for it, they haven't, so far as I know.
That said, it does include a real, full version of Internet Explorer (and real, full Flash) which is much better and faster than the stripped down versions of Firefox and Chrome available on Android.
Of course a full Windows 8 tablet like Surface Pro can also run full Firefox or Chome (in addition to programs from the Windows store).