Oh right, that!
v3 of Camen Design was released around about the launch of Firefox 3.5 (and fully took use of it), this meant that there was still a majority of users on Firefox 3.0 initially
Because of that, and the addition of CSS3 media queries in Firefox 3.5, I decided to layer CSS support in by creating a lo-fi theme first (Firefox 3.0 / no CSS3 media queries), and then using CSS3 media queries to adapt that to better browsers / printer / mobile &c.
So the "all" section is the shared layout of the page, the "lo-fi" section is the theme for Firefox 3.0 and the "hi-fi / desktop" section is the theme for Firefox 3.5+
It’s very complicated, but then I was using CSS3 media queries on a site the day they became available to the majority of Firefox users. :)
If you want to see what this "hidden" lo-fi skin looks like (it's quite beautiful in it's own right, and fully supported across all the content), just get yourself a copy of either Firefox 3.0 or Camino 2.0.