One of the great benefits of running Firefox is the multitude of third party extensions available. In any way you can imagine to alter or enhance the features of Firefox there is possibly an extension for it, and if not you can make one (given you have the expertise.)  Here is a list of the extensions I use regularly on Firefox and have found to be either fun or useful.

Adblock Plus

Ever been annoyed by all those ads and banners on the internet that often take longer to download than everything else on the page? Install Adblock Plus now and get rid of them.

BetterPrivacy

Ever wondered why you are still tracked though you tried everything to prevent it?
BetterPrivacy is a Super Cookie Safeguard which protects from usually not deletable LSO’s. It blocks longterm tracking on Google, YouTube Ebay and many other domains.

Video DownloadHelper

The easy way to download and convert Web videos from hundreds of YouTube-like sites.
This works also for audio and picture galleries.

Download Statusbar

View and manage downloads from a tidy statusbar – without the download window getting in the way of your web browsing.

DownThemAll!

The first and only download manager/accelerator built inside Firefox!

FEBE

FEBE (Firefox Environment Backup Extension) allows you to quickly and easily backup your Firefox extensions. In fact, it goes beyond just backing up — It will actually rebuild your extensions individually into installable .xpi files. Now you can easily synchronize your office and home browsers.

FireGestures

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

Flagfox

Displays a country flag depicting the location of the current website’s server and provides quick access to detailed location and webserver information.

Lazarus: Form Recovery

Never lose anything you type into a web form again! Lazarus securely auto-saves all forms as you type, so after a crash, server timeout, or whatever, you can go back to the form, right click, “recover form”, and breath a sigh of relief.

NoScript

The best security you can get in a web browser! Allow active content to run only from sites you trust, and protect yourself against XSS and Clickjacking attacks.

Read it Later

Read It Later allows you to save pages of interest to read later. It eliminates cluttering of bookmarks with sites that are merely of a one-time interest.

OPIE

Import/Export extension preferences

Screengrab

Screengrab! saves webpages as images… 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.

ScribFire

ScribeFire is a full-featured blog editor that integrates with your browser and lets you easily post to your blog.

StumbleUpon

StumbleUpon discovers web sites based on your interests, learns what you like and brings you more.

TACO

Sets permanent opt-out cookies to stop behavioral advertising by 84 different advertising networks, including Google, Yahoo, Microsoft, all members of the Network Advertising Initiative, and many other companies.

Xmarks

Xmarks is the #1 bookmarking add-on. Install it on all your computers to keep your bookmarks and (optionally) passwords backed up and synchronized. Xmarks also helps you uncover the best of the web based on what millions of people are bookmarking.