Mozilla send out word today that Microsoft's Windows RT (aka Windows 8 on ARM) will only support Internet Explorer. Technically third-party browsers will be able to run in Windows RT's Metro mode, but they will be so crippled as to be unusable.
At first blush this sounds like a classic ploy to stymy the opposition and regain market share — and for all I know, maybe it is — but there are also a few logical reasons for Microsoft’s decision. From the get-go, Microsoft has been leery of developers porting x86 code to ARM, in case these ported apps don’t have the efficiency and stability that a low-power (and battery-powered) ARM tablet requires. It’s for this reason that Microsoft didn’t offer some kind of OS- or hardware-level x86>ARM translation.
Browsers are also one of the juiciest attack vectors for malware — and also one of the most “visible” aspects of a modern operating system. If a user installs Firefox (or Opera or Chrome) on a Windows RT table, and then it gets bogged down with malware and toolbars, you are likely to walk away with a sour taste for Windows RT; “It’s just like Windows 7 damnit!” By only allowing Internet Explorer, Microsoft should be able to keep Windows RT running smoothly for longer. (This is the same reason that Apple doesn’t allow third-party operating systems on its iOS devices, incidentally.)