Getting started with Firebug

  I'm trying to figure out where the blank space is coming from in the layout of the scripting.com home page.
  People suggested using Firebug, so I installed it, and it looks great, but I have a basic question to get started.
  Here's a screen shot. What does the lime-green shading signify?
  That's the bit I want to nuke. I can't tell where it comes from.
  Update: Thanks for all the help -- I figured out what to do not only with the extra vertical space but with the help of Firebug, I now understand why text on the index pages was indented under the headings. I didn't want it indented. So I created a new class "showForIndexPage" and use it in place of "show" on the index pages. It has much more modest horizontal padding.
  Things are starting to line up the way I want them to. :-)