Start - Chickenfoot - Pentadactyl. Monkey see, GreaseMonkey do! - Pentadactyl. Start - Beat Any Website into Shape with Greasemonkey » SitePoint - Pentadactyl. Greasemonkey is a Firefox extension by Aaron Boodman, which allows you to run personal DHTML scripts (known as "user scripts") on any Website.
User scripts are essentially bookmarklets that run automatically, but because they do, they’re a whole lot more useful. Ever used a site that doesn’t work in Firefox, even though it could with just a few minor tweaks? Start - Tutorials - GreaseSpot - Pentadactyl.