Firefox's official roadmap has been updated, which brings interesting changes for the future. Most notably, Firefox 7 will ship in 2011. The second focus of Firefox development in 2011, is to make sure there is no more than 50ms between any user interaction and feedback from the browser.
As far as feature sets go, this is what the roadmap looks like: Firefox 5 will absorb the Account Manager and F1 Simple Sharing add-ons to become built-in features. It looks like Windows 7 64-bit will be officially supported with FF5, too.
Firefox 7's feature list is less clear. Electrolysis (splitting everything into separate processes) and changes to XBL support are mentioned, but nothing certain.
Overall, there's a big emphasis on responsiveness and "shining the primary UI until it gleams."