I want to know if Taskfox makes the final cut: http://geektechnica.com/2010/06/5-exciting-changes-coming-to...
I'm more concerned about memory leaks.
It is almost solved with the memory fox plugin, but I still need to restart Firefox 3.x every month instead of every week.
I hope that Firefox 4.x will address this problem.
Electrolysis (even more process seperation) merged with trunk recently: https://bugzilla.mozilla.org/show_bug.cgi?id=571166
Hardware accelerated graphics should be turned on by default soon as well.
And of course, the continued iteration of the new theme, many platform featured to be added...