Here are some helpful Firefox extensions
recommended by Smartlab Software. We use these nearly
every day in our web site improvements.
LinkChecker
Checks links on a web page. Colors the links green
if they are ok.
McAfee Site Advisor
Site advisor gives safety information whether a site has issues with it, such
as spyware downloads.
Session Manager
I use this one all the time. Session manager saves the previous three
sessions which can be reinstated.
ColorZilla
Point your cursor to a color on the screen and ColorZilla will tell
you the RGB and hex value of it.
Firebug
You can edit, debug, and monitor CSS, HTML, and JavaScript live in
any web page.
Lynx Viewer Tool
View a web page like a search engine sees it.