Cooliris (formerly PicLens) tries to bring a cinema-style viewing experience to browsing the web. It makes the most of your Mac's graphics card and RAM to provide a truly impressive experience.
Cooliris is a Firefox extension that places a button on the right-hand side of the toolbar. Pressing the button on a Cooliris-enabled site (currently not many but it does support Flickr, Yahoo!, Google and PhotoBucket) suddenly displays all of the photos it can find on a virtual wall. Using the mouse you can slide the wall left and right plus zoom in and out.
While Cooliris certainly makes browsing spectacular, it takes a lot out of your graphics card and RAM so it's not a good idea to use it with many other applications open. It's also questionable how useful it really is. Granted, the pictures and images look great but for general browsing, there's not much need for it. There are a few preferences for it, however, that allow you to customize it, although adjusting the slideshow speed is hardly the most important feature that most users would like control over.
Cooliris looks great and it's a nice idea but the fact that it's limited to a handful of websites and that it's resource-sapping mean that it won't be for everyone.