If youd like to run Firefox in both UIs, you can try the Windows 8 preview version available from Mozilla. Note that only your current default browser can run in the Modern UI. In my tests, if you selected a non-Modern UI browser as your default such as Opera or the current stable version of Firefox, that will turn off the Modern UI version of Internet Explorer.
Windows 8 vs. Windows RT
There are two versions of Windows 8 to choose from. Which one you get depends on the device you intend to buy.
If you purchase a new Windows tablet with an ARM processor, then you get Windows RT. If you dont know what an ARM processor is, look for tablets with processors from Nvidia or Qualcomm: those are RT tablets.
The difference when you buy an RT tablet is that it is not capable of running legacy Windows apps, even though an RT tablet includes the traditional desktop interface. An RT tablet can only run downloadable Modern UI apps from the Windows Store.
You cannot download Windows 7 versions of AIM, Dropbox, Skype, or Spotify. If its not a Modern UI app from the Windows Store, then you cant use it on Windows RT.
If you dont mind being restricted to the Windows Store, you should be able to pick up a Windows RT tablet for a good price. Microsoft on Thursday said there would be some Windows RT devices priced as low as $300.
If you have a Windows 8 device with an Intel or AMD processor, including old Windows PCs, you can run any app from the Windows Store and pretty much any program written for Windows 7.
Dont forget to right-click
Because apps in the new Modern UI are fairly minimalistic, a lot of functionality that used to be available at the click of the button such as preferences, save, and upload are hidden.
There are two ways in Windows 8 where you can typically access this functionality from a PC. One is by right-clicking. This will immediately call up a menu bar at the bottom of the screen with a few options.