I'm always trying to find new functionality of Firefox's extensibility - admittedly uninstalling most of the add-ons through lack of need. However I really like the useful ones that just integrate.

Here's three new ones I'm using at the minute - might come in handy for you too.

Minimap Sidebar is a handy tool that can be used as a sidebar or in a tab, drag location or address into the Multimap page to make the map load or enter locations by typing it in. Also adds contextual menu item.

UrlbarExt adds commands to your location bar giving you the options to copy url, use tinyurl to shorten the url, tag pages, browse anonymously and search the site you're on.

Juice can act as a search sidebar for rich content and your google searches.