Firefox 2.0 is not even officially released and yet the Mozilla developers are hard at work... on 3.0. Not to imply they are shifting focus away from 2.0, they are actually soliciting the community for features and suggestions you'd like to see in the next version. Since we already have an idea of what 2.0 will bring via the current betas, the dev team wanted to look for what users might be after. As such, they've setup a Firefox brainstorming wiki for the task. The current list is truly behemoth, dozens of pages long. Some of the requested features include site trustworthiness (perhaps akin to the Netcraft toolbar), an automatic update mode, asynchronous DNS lookups, and a whole lot more.
Their future goals are to do a core redesign of the browser, moving to a platform that would enable functionality on smart phones and other embedded devices. The list is definitely worth browsing.