Lack of a Better Word

Firefox allows you to go deep into the code visually – specifically into the nesting of tables and divs. How?

First right click on an area. You will see the choice to ‘Inspect Element’. In this case it is to look at the profile picture in this Facebook timeline.

Now at the bottom of the page to the right you will see the button for ‘3d View’

When you click that, you will be able to move your page around as so, allowing you to choose the divs and understand how the page is built.