If you are developer and dont know what Firebug is then shame on you.  But for those of you non-code folks, Firebug is an add-on for Firefox and is hands down the best developer tool available.  Its simple to use and lets you make live edits to your css, html and javascript.   I cant tell you how many hours Firebug has saved me over the years when dealing design issues.  Thank you Firebug and your glorious goodness.