Created attachment 41897 [details] reduced test case Was sans-serif in Safari 4.0.3, is a serif in ToT. Looks like CSS font fallback has changed.
Looks like there was a bug in 4.0.3 (and maybe earlier): the inspector shows a computed value of 'foobarbaz, Tahoma, sans-serif' for the font-family property on the pre element, which is wrong.
Firefox uses a serif font, too.
A funny thing is that Firefox also uses a sans-serif font on my machine - apparently, this depends on system primary language. IE and Opera also use sans-serif, because they don't follow CSS spec correctly. We probably don't want to drop spec compliance just because of one site, especially since Firefox only works by accident, and the symptom is extremely mild (and may even bee seen as an improvement by some). From past experience, evangelizing this site doesn't work, so closing as wontfix.