The extension provides "Status Text", "Progress Meter", and "Download Status" items. These toolbar items can be moved wherever you want by customizing the toolbars. Behavior of the toolbar items, and other additional settings, can be controlled in the extension preferences.
This extension can also act as a replacement for the Fission extension. There are preferences to show links, status, and progress in the location bar instead of the toolbar items.

Edit textareas using an external editor, because it's all text!
Right click on a textarea, select "It's All Text!" and edit the text in the editor of your choice.
Alternatively, click on the edit buttons added for your convenience. Right click on the edit buttons for even more options, including preferences.

Google Search has the annoying habit of changing the result link when you click it. If you try to copy the link you get some gibberish instead of the actual link. This extension disables this behavior - on any Google domain, without having to configure anything. Simply install and enjoy!

Changes the selected search engine in the search bar by scrolling the mouse over the searchbar or search context menu. Also supports keyboard shortcuts ctrl+k and ctrl+shift+k to change the search engine with the keyboard.

This add-on replaces the standard download text of Firefox 3.* with some more detailed information. It displays the total download speed, the remaining size, the total number of files and the remaining time of your downloads (including DownThemAll!).

Yahoo!'s Exceptional Performance team has identified 34 rules that affect web page performance. YSlow's web page analysis is based on the 23 of these 34 rules that are testable. Click each performance rule below to see the details.

Adds a "File" menu option to open multiple locations at a time.

BlueGriffon is a new WYSIWYG content editor for the World Wide Web. Powered by Gecko, the rendering engine of Firefox, it's a modern and robust solution to edit Web pages in conformance to the latest Web Standards.

Show the font of selected text in the context menu.

Shows a tooltip for all links, folders, bookmarks and RSS items on Bookmarks Toolbar, Bookmarks Menu', History Menu' and also Sidebars!
You can also see the last visited date, tags, description and the keywords!

Firebug extension to view which CSS rules are actually used.

Search bar optimized for quicker switching of search engines.

Changes the Location Bar of Firefox into a Breadcrumb display with rich and interactive features.

A customizable mouse gestures extension which enables to execute various commands and user scripts with five types of gestures.

Extends the function of the drag-and-drop mouse gesture so that it can be used to load URLs, do a web search of selected text on a page, or save an image on a page. Compatible with both Firefox and SeaMonkey.
This is the successor to the defunct SuperDragAndGo extension; it delivers the same functionality with a small footprint.

Add sub-menus to History Menu for previous days' history.

Type anywhere and use the awesome bar straight away!

The location bar is often called the Awesome Bar because it’s great at remembering websites you’ve been to and guessing where you are trying to go.

var evt = document.createEvent("KeyEvents");
evt.initKeyEvent(
"keypress",
true,
true,
null,
false, // holds Ctrl key
false, // holds Alt key
false, // holds Shift key
false, // holds Meta key
evt.DOM_VK_F5, // presses a special key, @see http://mxr.mozilla.org/mozilla/source/d ... yEvent.idl
0 // presses a normal key, e.g. "A".charCodeAt(0),
);
document.documentElement.dispatchEvent(evt);

It will capture what you can see in the window, the entire page, just a selection, a particular frame... basically it saves webpages as images - either to a file, or to the clipboard. It captures Flash too!