FWIW, I just went to your site and it all displayed correctly. There was another report that related to Firefox font rendering doing some similar (though not as drastic) things, so I suspect it's the same issue. Unfortunately, I really don't know what that issue is.
That happened on my installation too! Drove me nuts! I saw everyone elses admin page looked fine. It cleared up on upgrade to 1.5, though. I look normal again! BTW, it was "only" the Admin login page that did it.
Something you might want to check is if Google's mod_pagespeed is installed on your server and what version it is. I accidentally had the beta version installed on a server and it started wreaking havoc with displays. Sometimes everything was fine, and sometimes it wasn't. Once I removed the beta version all worked as it should again.