Once again, the problem here is that if you do that, people will scream HEY WHERE'S MY MONA I SET MY BROWSER TO USE MONA FOR JAPANESE, and if you change it to font-family: "Mona", "MS Gothic", sans-serif; it'll be HEY WHERE'S MY MS GOTHIC &C &C &C.

world4ch tried, and people screamed their heads off right away.

What you can do, though, is get a Firefox extension (I forgot the name... orz) that adds an id field containing the URL to each page, so that you can override styles and fonts for different pages in your userContent.css file.