What is a hack, by Paul Rouget:

So, “just for fun”, and to show how far you can go with the extension mechanism, here is a little useless extension I wrote: a Nintendo Wiimote driver for Firefox.

What does it do? It brings Wiimote events to web content. You can change tabs with a “forehand/backhand” tennis drive and, in your web page, make your elements move using Wiimote events (rotation, g-force, position, etc.). Web pages, of course, do not support this API. But, with another extension, such as a Jetpack or Greasemonkey, you can “hack” a website to add support for the Wiimote.