Q1208 How can I detect a change of URL in my pop up window?

If both pages are from the same server then in the popup window:

<body onUnload="opener.tellMomma()">

and in the opener window:

function tellMomma() {
   alert('Child changed');
}

var WinId = window.open('popup.htm')
if (!WinId.opener) WinId.opener = self;