Installing this theme isn't quite as simple as you are probably used to—you'll need to first enable the All-Glass Firefox extension for the Aero effects, the Personal Menu extension to hide the menubar and add the Tools button, the Stylish extension for a tweak that fixes the text, and then drag the mockup theme's *.jar file into the add-ons window to install it.Personally, I just downloaded the theme from Boneyardbrew's page and it looks fine to me, minus the tweaks that the other add-ons provide.
Once you've successfully completed all of the steps—which are detailed on the download page—you should have an impressive browser style that looks very similar to the screenshot.
Enjoy.