Download YouTube Videos as MP4 and FLV
Adds a download button to your youtube video page

DownThemAll!
The mass down loader for Firefox.

Firebug
Web Development Evolved

Google Image Help
Tired of opening every small image in google search by clicking two times to get full sized image.Adds a new item to Right click drop down menu "Open full size GOOGLE image" from which you can select page number and a new tab will open with all full sized image with it

Hide My Ass Proxy Extension
Extension for Hide My Ass proxy service More

User Agent Switcher
Adds a new menu item under TOOLS from which you can browse as mobile,Iphone etc