Whether you’re a professional web developer or just the guy living across the street making his own web page to show off his collection of vintage 80’s mini crotch rockets, then you need the Web Developer tools for Firefox.
Web Developer puts a plethora of information about a page within a single click of a mouse.
View css, outline how the elements stackup, image widths, display the paths to links, paths to images, hide images, and so much more. You can even edit css of a page live!!!!
To get the Web Developer you can either go Tools>Extensions>Get More Extensions from Firefox or go to the Firefox Extension page.