[yohui]

> The restriction is only in place for Windows RT apps, of which Microsoft has a rather negligible marketshare of the tablet market.

The restriction against using browser engines other than IE's Trident applies to "Windows Store Apps" for desktop, too.

Mozilla and Google managed to claw out a half-hearted concession for the browsers themselves on the desktop (though not RT), but even then the other restrictions that mbrubeck noted still apply: the browser needs to be installed outside the Windows Store and only the default browser is allowed to present a touch interface. I'm not sure what purpose is behind the latter restriction, other than making switching or experimenting with browsers slightly more of a hassle.