Using Aardvark Firefox extension
I wrote this post a while back. The content can still be relevant but the information I've linked to may not be available.
Following on from a previous post, another tool I have been using recently is the Aardvark Firefox extension or add-on. When Aardvark is turned on in Firefox, it enables you to see the webpage structure when you move your mouse. Block level elements and their class names (if present) are outlined in red as your mouse moves over each webpage element, which makes it easy to see which elements and styles are used.