If you have anything to do with CSS/XHTML and web design, Chris Pederick's Web Developer extension for FireFox is a must have! It lets you do a whole bunch of things directly within FireFox, including:- Display CSS stylesheets used by a web page- Edit the CSS sytlesheets directly and see the web page change as each change is made- Edit HTML- Disable CSS stylesheets- Display image file sizes   read more »