If you need to debug JavaScript or CSS you can do it in different browsers:
  • Mozilla Firefox - install the firebug extension (to open it click F12).
  • Microsoft IE8 - go to Tools>Developer Tools (or click F12)
  • Google Chrome - go to Page > Developer > Developer Tools (or click Ctrl+Shift+J)
These tools are great when you need to test small changes to the HTML and CSS or when you need to debug a problem in JavaScript.

Cheers,
Tiago Simões