I'd like a way to kill the fucking "smooth scrolling" that occurs when I MW scroll the tab bar. It's skippy, slows things down, doesn't really look good, and generally needs to die.
I use Forecastfox, NoScript, Greasemonkey, Aardvark, Firebug, Adblock Plus, PDF Download, Oldbar, DownThemAll! (for when I want to download a bunch of files by a mask, such as all links matching "*.mp3" in a directory), sometimes Torbutton and Stealther :eloH:, and maybe a couple others I'm forgetting.
I use the Firefox Vista theme, because the XP one is uglier, IMO. I'm pretty pleased that the default Firefox 3 themes didn't look shitty, the way they did in 2. I used to use Winestripe for the old Firefox theme.
(Also, I've been having better experience with Opera 9.5 than I was with 9.2. The default theme is prettier and, more importantly, seems to be a bit better behaved with different color schemes. Also, they finally killed that detestable bullshit in which when I used middle-click to pan a page, it would spawn the panning anchor in the middle of the web site, instead of where I middle-clicked.)