Firefox on Nokia N900 is available as a public beta, version 1.1 now. Nokia N900 is based on the latest Maemo platform and Firefox is solely being developed for the N900 currently extensively.
Firefox 1.1 beta features the same engine as that of Firefox 3.6 for the desktop. The mobile version of this browser features auto-complete on forms, a new context menu to open new tabs and save images. You can add search engines and save a we-page as PDF in the browser by default. This makes Firefox even more awesome.
This video will give a better impression.