View HTTP headers of a page and while browsing.
The original Gmail notifier for multiple accounts. Allows you to receive new mail notifications along with viewing account details including unread messages, saved drafts, spam messages, labels with new mail, space used, and new mail snippets.
AutoPager automatically loads next pages when you reach the end of a page. It works on a ton of sites,Google,Yahoo..
It works well with most other add-ons adblock plus, WOT and most of the greasemonkey scripts.
You can also try AutoPagerLite.
A Statusbar with speed, percentage, time and loaded size (similar to Opera's one)
Customize application menus:
Rearrange or remove menuitems from the main context menu (right-click menu) and main menubar (File Edit View etc.)
A complete redesign of popular Google services, Google Redesigned changes the appearance of popular Google services.
Gives a possibility to create custom toolbarbuttons...
Note from Mozilla: This add-on has been discontinued. Try FXChrome instead.
Chromifox Basic is a coat of chrome for Firefox.
Extends the Location Bar with set of commands to (Shorten URL's,Copy URL,Search site,Go up, pNg, Tag pages easily ,Navigate through sequential URL's,View page cached version,Surf anonymously using online phproxy servers, Twitter)
Collections are groups of related add-ons that anyone can create and share.Explore Collections