Browser extention to aid Web Developer

Internet Explorer Developer Toolbar
http://www.microsoft.com/downloads/details.aspx?FamilyID=e59c3964-672d-4511-bb3e-2d5e1db91038&displaylang=en

Top 10 Must Have SEO Firefox Extensions!
http://www.pagetrafficblog.com/top-10-must-have-seo-firefox-extensions/2662/