PC and Macintosh Javascript differences

I have a script which works fine under IE and Netscape on a PC, but doesn't work on a Machintosh. Does anyone know of any thing Machintoshs need done differently than PC's for Javascript.

Here is the script, it just moves a Flash files frame position.
<!-- Hide JavaScript from old browsers
var InternetExplorer = navigator.appName.indexOf("Microsoft") != -1;
var targetFrame = 0;

function syncframe(frame) {

var buttons = InternetExplorer ? window.navmovie : window.document.navmovie;

targetFrame = frame-1;

if ( buttons != null )
window.document.navmovie.GotoFrame(targetFrame);
}

-->