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

Question

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 need to check it on Windows with Firefox 3.6?

Answer 1

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