Personas are free, easy-to-install "skins" for Firefox. Personas Plus extends that built-in functionality to give you even more control and easier access to new, popular, and your own favorite Personas.
Useful tools for the nightly tester.
Show less chrome by default unless it's needed
An extension that allows for the use of dynamic commands in Firefox.
Fill in the rest of words as you type them into the location bar
Start loading pages as you select them from the location bar suggestions
Jetpack Prototype is an experiment in making it easy to build Firefox add-ons using common web technologies.
Find stuff instantly from a dashboard that appears over a full-window browsing experience.
Display some information about your past search behavior
Snowl is a Firefox extension that helps you follow and participate in online discussions. It supports Twitter (including multiple Twitter accounts) and it makes it easy to subscribe to and follow feeds in one of several views.