The FaceBook Web Designers have a certain look to their website that they'd prefer you see it as. This is an extremely quick & easy way to make sure you're seeing it that way too, because chances are you aren't already.
It's a simple matter of installing the font they designed FaceBook in on your own computer so the pages are rendered using it. Here's how to do it:
By simply copying the font to that font folder, it'll install and register it with your system, and from then on out anytime you view a FaceBook page, you'll see it the 'proper' way.