I won't post the url's as you can find them all on the add-on page with a simple search...
https://addons.mozilla.org/en-US/firefox/
Adsense Preview
Clippings
ColorZilla
DOM Inspector
DownThemAll!
Fasterfox
Firebug
FireFTP
Font Finder
GetVideo
Google Toolbar for Firefox
IE Tab for PC and IE View Lite for Mac
iWEBTOOL Webmaster's Toolbar
JSView
MetaTags
NikkelWHOIS!
NoScript
Password Exporter
Professor X
Safari View
Screen grab!
SearchStatus
SEOpen
SeoQuake
Server Spy
Web Developer
Window Resizer
Add to the list..................
