I added a bug upstream earlier. In safari 3.5 and 3.6 if there is no line-height defined specifically in your css for a pre (or maybe the body tag) then one of the functions in the line-highlighter returns NaN (safari returns the text string normal, whereas firefox performs a calculation based on its defaults and returns a number) when it should return a number.
the easiest fix is to add a line-height definition to the pre tag in the prism css files.
this is just for info. not sure if you want to fix it. I think most people who use a reset css would have this covered. On the official prism site, the styles.css (which have nothing to do with prism have a definition so the examples on screen work but the downloaded files don't).