IFRAME in PC and MAC

I use the following HTML Statement to embed a IFRAME in my webpage.

Later I change the content of the IFRAME by loading another file into the IFRAME using the following Javascript:

function loadPage(pagename) {
document.contentframe.location = pagename
//more code for extra functionalities...
}

This Javascript is called by buttons placed on the page. This works perfectly in PC. But in MAC, it doesn't work. Can anyone suggest a workaround?

Thanx for your time.