Web Developer extension for Firefox is a lifesaver !

I might be the last web developer on earth to find this extension but just in case you haven't discovered it yet do yourself a favor and go install it immediately. Not only does it display any possible form of information on your pages STRAIGHT ON THE PAGE, it is a serious helping hand on CSS and JavaScript debugging, it has validators for all sorts of stuff, it even resizes the browser to 800x600, now if you don't find any of the above a tad useful clearly you're not in the business.
Go fetch boy, go!