Firefox iterations have made just about as much sense as any other major software suite, with a jump from 1.x to 1.5.x to 2.0. That won't be changing, and Mozilla has had long in progress Firefox 3.0. It, much like the change to 1.5 was, will come as a very marked jump from where 2.0 sits today. If you're curious as to what exactly they have in store, there's an inside look at the future browser and what sort of changes they will be offering. Among the big key improvements may be the inclusion of offline Web application support. This is key, because many companies, including Microsoft and Google, have been experimenting with web applications on the desktop for quite some time.
The article goes further in depth as to the importance of local web application storage, as well as what role Firefox might play in the market that will no doubt soon be dominated by Vista desktops. Another interesting feature in store will be a localized SQL database that will store personal browser data, making it easier and more flexible to use with search tools or make development easier. It is quite a long read, but reveals some interesting developments for the increasingly popular alternative browser.