I'm trying to use Chris Pederick's agent switcher along with Firebug on Firefox, but no matter what I set it to, localhost/ is still showing the desktop version of the site. What are some common errors I could be making here? I'm trying to locate which style-tags in css/mj_xhtml.css are making the navigation items overlap vertically, making them difficult to 'click' on. Any help is greatly appreciated!

Hi,
Please try to clear cache on the browser and also clear cookies (both domain and session).

Here are some more ideas on how to use Firefox to see the mobile view.
www.mobilejoomla.com/forum/3-general/5212-display-as-mobile-version-on-firefox.html#5213
Hope that helps.