My Favorite FF2 Tip
The first time I needed a tip for Firefox 2.0 was to make its tabs have the close button "like before" (and I was pointed to kb.mozillazine.org). Now I am using the default FF2 behavior and I feel a little awkward with the classical one.
Stuff like network.dns.disableIPv6 is old news for most people, and tweaking various other network config variables doesn't bring much. So I was not thrilled by Speed Up Firefox web browser.
What I welcomed warmly was another collection of FF2 tips and tricks: Random Firefox Tweaks.