Memory consumption is really important in a web browser. Firefox has some room for improvement on that front, and so Jeff Muizelaar and I are working to start up an effort, called “MemShrink”, to reduce memory consumption in Firefox 5 (and beyond).
We’ve started a wiki page outlining some ideas on ways to improve our tracking of memory consumption. Please read it and comment.
I’ve also opened bug 640452, which is a tracking bug for memory leaks in Firefox 5, and bug 640457, which is a tracking bug for other memory improvements in Firefox 5. Please CC yourself if you’re interested.
Update: I just added bug 640791, which is a tracking bug for improvements to memory profiling.