Cross browser testing - same browsers differ on mac and pc?

For cross browser testing do I need to test the same versions of browsers on both Mac OS X and Windows?

For instance if a site works fine on Firefox 3.6 on Mac OS X, do I also 开发者_Python百科need to check it on Windows with Firefox 3.6?

Ive never run into trouble by relying on testing it for only one os per browser,

Except that sometimes fonts may be missing depending on the os.

EDIT: Apparently fonts are an issue but there might be more, as explained here, so you might have to test cross-operating systems

I had an issue with Opera for mac messing up javascript on my site when I used @font-face but the PC version was fine.

Same browsers versions for different OS never give an issues unless and until you encounter with animated feature. Color would be a little variant. Also the images may appear stretched in MAC OS. Rest would be good to go !.