Among the many Firefox extensions out there, there exists Firebug and it is good. It is truly an amazing piece of software. There is a CSS(cascading style sheets) viewer, so that when you inspect an element in the DOM(document object model), you can view all of the CSS attributes that apply to that element. Not only does it show you the applicable CSS rules, it breaks it down to the styles being used and to the styles which have been overwritten. Very nice. There are many other things it does, but one feature in particular that I don’t think I would want to live witout is the console API(application programming interface).