I can’t stress the value of the “Web developer toolbar” for firefox. This plugin takes the pain out of css and gives you direct access to tools that make it much easier to see what is going on with any website you are creating. The toolbar has so many great features that I won’t take the time to explain them here.
The one I find the most useful is the CSS view style information option. As you move the mouse around a webpage is creates a red outline and corresponding text to tell you what css is effecting that particular section of the web page.
Robbalman