Kirish found the egg. So a cookie to him.
The weird CSS is intentional and is used to hide elements from graphical browsers. The text indent method is known as Rundle's image replacement technique. The other method is the Fahrner image replacement technique (though I'm not replacing an image).
The reason I used the first is because I dislike images in the design that serve no purpose in the content. So the FIRST logo is inside a text link that is hidden unless you are using a screen reading program or text browser.
The FIR is used to put a "Skip Navigation" option in a top menu. I ended up not using a top menu (the sidebar markup is all at the bottom of the html document), but the class got left in the CSS. The skip navigation link is only used for text browsers where a long menu at the beginning of a document can be annoying.
There is a problem with FIR where some screenreaders will actually interpret "display:none;". However, that's not really a problem with just a skip navigation link.
Here's a related article that might be helpful:
http://www.stopdesign.com/articles/replace_text/