General Use

Adblock Plus and Adblock page element hider

Blocks banner ads, popups, unders, flash, overlays, interstitials...

BugMeNot (From Roachfiend.com, you'll need to authorize this site to install the plugin)

This generates generic but working logins for many news and web sites requiring you to log in (NYT, LATimes, etc.)

Linkification

Converts unhyperlinked URLs to links

Nuke Anything (Enhanced)

LEts you remove any object/image/table/etc. from a page - great for printing!

CacheIt

Lets you view cached version of a site using gCache and WayBackMachine

TableTools

Ever wish you could sort tables in websites like you do in Excel? Export them to CSV/XLS? Filter the list or search through it? TableTools does this and more.

User Agent Switcher

Lets you fool websites which think they require IE

VideoDownloader

Extracts video from most flash sites (e.g. YouTube)

LongTitles

Shows the full title of an image on hover, instead of cutting it off

del.icio.us bookmarks

Integrates your bookmarks with del.icio.us

PDF Download

Always ask whether to open or download a pdf link

Forecast Fox

View the weather forecast

torbutton

Easily activates/cancels use of your tor proxy, requires TOR

GreaseMonkey

Lets you download or create custom actions for websites, like removing custom designs from all myspace pages.

Web Developer Toolbar

Everything you ever wanted to do as a webhead - live css editing, block/div/table outlining, resizing, etc.

ColorZilla

Extracts a color from images/backgrounds/text elements

LeetKey

Lets you encrypt/decrypt text, ROT13, and change case

Firebug

debugging tools for html, css, js...

TestGen

Record and replay actions (untested)

WMLBrowser

Lets you surf WAP pages

MeasureIT

Measure distance, width/height anywhere on a page

Image Zoon

Zoom in on any image