NOT ON THE 2014 LIST
The Web Developer add-on for Firefox adds a menu and a toolbar with various web developer tools.
Comments from some of those who selected Web Developer as one of their Top Tools
“Great extension for Firefox that should be available in every other browser. It’s useful for debugging XHTML/CSS sites. Greatest timesaver is a feature that allows me to create CSS quickly LIVE without reloading pages” Teemu Arina
“The Web Developer toolbar is my favorite!” B J Schone