Firefox compatibility was in the works but it just proved too difficult. Firefox doesn't adhere to OS X's configuration standards, so if NetShade was going to work with Firefox it was going to be a messy hack. If you prefer Firefox's HTML engine to Safari's, Camino is a good solution because it uses the Firefox HTML engine but is built Mac-style.
The screenshot on this site is in 3D view mode. There's a little button in the bottom left called "view mode" which toggles modes. That's probably why your NetShade doesn't look like the screenshot.