Blocks annoying video ads on YouTube, Facebook ads, banners and much more.
Adblock Plus blocks all annoying ads, and supports websites by not blocking unobtrusive ads by default (configurable).
Never be annoyed by a Flash animation again! Blocks Flash so it won't get in your way, but if you want to see it, just click on...
Tab Mix Plus enhances Firefox's tab browsing capabilities. It includes such features as duplicating tabs, controlling tab focus, tab clicking options, undo closed tabs and windows, plus much more. It also includes a full-featured session manager.
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.
LeechBlock is a simple productivity tool designed to block those time-wasting sites that can suck the life out of your working day. All you need to do is specify which sites to block and when to block them.
One click to clear your cache, cookies, history, html5/local storage, http logins, all of them or restart your browser with/without notifications.
Manage form history entries (search, edit, cleanup, export/import) and easy text formfiller.
Auto-save text entered in any form while typing to allow fast recovery when disaster strikes.
Control for which webpage form history is saved or not.
Open Bookmarks/History/Homepage/URL/Search in new tabs, and more utilities for tabbed browsing, including Protect/Lock/Faviconize/Unload Tab, Reload Every, Select and manipulate multiple tabs simultaneously, Tab Stacking/Coloring, etc.
Finds HTML elements matching chosen CSS selector(s) or XPath expression
Search/browse/shop faster than ever! Ctrl-Shift-F for whole-word/regex/all tabs/diacritic search;create custom engines;shopping assistant compares price;Smart SearchBox;Preview results;Auto copy plain text, dnd save image/open link.Use v3.363(below)!
Firecookie is an extension for Firebug that makes possible to view and manage cookies in your browser
Firecookie is part of Firebug since Firebug 1.10