This video shows the new Firefox's multitouch API that is available to web content, starting from the beta 3 preview of Firefox 4.
At the beginning of the video, you'll see how a webpage can get data about multitouch input, correctly track points of contact and differentiate between touch input and pen input.
At the second part, you'll see a visual application of multitouch input on a fluid simulator, where each point of contact adds a particle source, and the movement adds forces to the field.
Both parts use HTML5's canvas element to render their content.
You can read more about multitouch in Firefox 4 at hacks.mozilla.org