jQuery addClass question

jQuery addClass question

This is nasty but at least I have the variables I want, yes it's the old Firfox on a MAC issue.

So I know what OS and what browser is being used what I want to do now is to add some class names to the body tag.

<script>
$(document).ready( function() {
 if OSName = "MacOS" && browserName = "Firefox" {
  $('body').addClass("mac ff");

 if OSName = "Windows" && browserName = "Firefox" {
  $('body').addClass("win ff");
});
</script>
</body>
</html>

as a guess I think I need to add on onLoad somehow and I am not sure how to, help most appreciated.