With Firefox 3 settling down nicely in the browser world, Mozilla is already in the process of working towards v3.1 - code named Shiretoko (what's Shiretoko?).
Tab switching is one of the most prominent features that has been announced in the new release. According to Mozilla, while this feature does replace the Ctrl-Tab addon, the foundation of this feature is based on the code from this very plugin (so kudos to Dao Gottwald).
Personally the add-on that I would really like to see integrated into Firefox at some point in time is Adblockplus. I am strongly of the opinion that Ad blocking should be fundamental to a browser. Do you have any favourites that you would like to see integrated into Firefox?