MacBooks and Thinkpads already have all the hardware they need to know which way they're tilting, but most software don't bother to ask. Now, with the orientation-aware Firefox 3.6, your accelerometers might finally get some exercise.
Apple and Lenovo generally include the sensors as data protection tools: using readings from an inbuilt accelerometer, a laptop can recognise when it's in freefall, and spin down, or even cushion, its hard drive to try to minimise platter death. It works, sometimes! But on a hardware level, these accelerometers are just like the ones in your mobile phone, meaning they can track orientation finely enough to play simple physics games, which you'll evidently be able to do in the next version of Firefox:
Originally built as something that we would include for our upcoming mobile browser release, we've made it available on desktop systems as well. Many modern Macbooks and Thinkpads contain devices and drivers that expose this information. We've added support for Linux, Macs and some Thinkpads where drivers and devices are available.
So it was an afterthought for Firefox proper, and you'll have to code special games and sites for it, and it'll only work on a few major laptop models. It's not exactly The Future of Firefox, but it's a cool trick nonetheless.