*With the recent update to Firefox 4, some Add-Ons are not compatible at the moment.
**ADD-ONS THAT EVERYONE SHOULD HAVE**
Adblock Plus - Annoyed by adverts? Troubled by tracking? Bothered by banners? Install Adblock Plus now to regain control of the internet and change the way that you view the web.
Anonymouse - Right click on any link (NSFW especially) click "Open Anonymously", and it auto proxys it in a new tab, even if that site is blocked. *I recommend using the ad remover script below, via Greasemonkey*[LIST]
Anonymouse.org Remove Banner - Removes the anoying banner ad that follows you on every page while using Anonymouse. (This is a script for Greasemonkey - For more information, look below)[/LIST]
AutoPager - AutoPager automatically loads next pages when you reach the end of a page.
Download Statusbar - View and manage downloads from a tidy statusbar - without the download window getting in the way of your web browsing.
FastestFox - Highlight anything, and with one click, autoseach it in Google, Youtube, Twitter, Wikipedia, etc. *Super useful*
Greasemonkey - Customize the way a web page displays or behaves. Some of my favorite scripts: (Found at userscripts.org/)[LIST]
[*]Better Amazon - Removes Ads, cleans the page, makes sections collapsible, adds Amazon Average Rating to the title, and packs lots of information into one screenful!
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[*]My eBay auto-forward - Script to forward the browser from the my-ebay guest page to the real page.
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[*]My eBay autologin - Automatically submits the My eBay login form (and checks the "Keep me signed in" box) if your username and password were automatically filled in.
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[*]No MSN on Hotmail Signout - Stops hotmail redirecting you to msn when you sign out
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[*]Windows Live Ad Remover - Removes the ads from Windows Live Mail (Hotmail).
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[*]Youtube "Lights Out" - Turn the lights out for easier watching of YouTube videos!
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[*]Youtube Auto Buffer & Auto HD & Remove Ads - Buffers the video without autoplaying, removes in-video ads, and puts it in HD if the option is on.
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[*]Youtube Cinema Size Enlarger - Autoscrolls Youtube player to top and resize the video to a nice and comfortable size.
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[*]Youtube Simple Links - Removes unnecessary parameters from links like feature=channel.[/LIST]
Hotmail Watcher - Watch for your new Hotmail and report to you in status-bar. Check Hotmail at specific interval. Neither username nor password is need. No sensitive information storage.
ImageShack Right-Click - Right click on an image >> "Upload to ImageShack"
LastPass Password Manager - Free online password manager and Form Filler that makes your web browsing easier and more secure.
McAfee SiteAdvisor - With SiteAdvisor you can search website safety reports, site ratings and community reviews from the McAfee SiteAdvisor website.
Rights To Close - Close your current tab by simply double right clicking anywhere on the screen.
SkipScreen - Skips unnecessary pages on sites like Rapidshare, Megaupload, zShare, Mediafire, and more. 
SmoothWheel - Scrolls the page smoothly when scrolling the mouse wheel (or keyboard arrows if enabled).
Speed Dial - Direct access to your most visited websites
Tab Mix Plus - 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. 
Toolbar Buttons - A button pack for Firefox, Thunderbird and Sunbird.
Classic Compact - A very clean and compact theme with classic arrow buttons that minimizes space consumed by menu, tool, tab, find and status bars without hurting the overall usability. 
Favicon Picker - Change your bookmark icons! Right-click a bookmark, and select "Properties", then "Browse" for a new image or paste in a URL.
Multirow Bookmarks Toolbar - Your bookmarks toolbar uses multiple rows instead of having a drop down menu. MyWords - Handy extension that can be used to save common words and phrases you use often for easy typing.
Tiny Menu - Replace the standard menu bar with a tiny menu popup.[Updated 5/15/11]
nice post
