YSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages.
http://yslow.org is the official open source website.
This extension provides advanced configuration for your browser and many additional options, that are not displayed in the Firefox "Options..." dialog.
CLEO (Compact Library Extension Organizer) is a Firefox extension that works with FEBE* to package any number of extensions/themes into a single, installable .xpi file.
Launchy will enable you to open links and mailto's with external applications...
Adds advanced search capabilities to the Firefox address bar. Supercharge the "Awesome Bar" with instant search results that appear as you type!