Extensions

Linky

Open Selected Links In Tabs. I cannot live without this extension.

FireMule

Open ED2k links properly

Hash Coloured Tabs

Group tabs from the same website together

Image Assistant

Open This Image In PaintShop Pro

Reload Every

Reload this tab every $foo seconds.

Add & Edit Cookies

Artificially extend the life of your session cookies

Greasemonkey

Because it’s Greasemonkey

HTML Validator

Validation Is Good

Disable Targets For Downloads

Stops binary files being launched as empty tabs

Google Preview

Thumbnails of the site you’re about to visit

Session Saver

Get back to where you once belonged

Web Developer Toolbar

Edit CSS. Disable Styles. I use this daily.

PDF Download

Stop firefox opening PDFs inline

IE View

Because you still have to test it

Tabbrowser Preferences

Happiness is a configuration window.