Totalidea, the folks that brought you TweakVI, and Tweak-XP Pro have a Firefox "tweaker" now that optimizes your Firefox settings.  It's called FireTune and is pretty nice.

I have one minor complaint.  The "check box" below labeled "Create backup of configuration" isn't actually a check box.  It's a button to create your backup.  You'll want to push that button before you do anything.  Other than that, no complaints.