An intern at the Mozilla Foundation by the name of Felipe Gomez has, in a spare lunch break we assume, built a multi-touch interface for Firefox and produced a video showing the cool stuff that you could do with such a technology.
He demonstrates moving objects around, drawing, selecting areas of an image, resizing, and two people playing "pong" at the same time on the same screen. With touchscreens on proper computers being poised for widespread adoption, such a tech could prove useful.
Can you think of any other cool stuff that you could do with a touchscreen interface on a web browser? Share your ideas in the comments below.