PicLens is a browser plugin that delivers an immersive full-screen experience for viewing photos on the Web. It’s currently available in beta for Firefox 2.0 on Windows and for Safari on Mac OSX. Support for more browser / OS combinations is underway!
There are hundreds of plugins available for Firefox in the Firefox plugin gallery. Only 26 of them are on the Firefox recommended list. Only one vendor/developer has more than one product in that list of 26: CoolIris.