...
var unloading = false;
...

function resizeContainer() {
    if (!unloading) {
        window.parent.document.getElementById("xxx_div").style.display = "none";
    }
}

$(window).load(resizeContainer);
$(window).resize(resizeContainer);
window.onbeforeunload = function () {
    window.parent.document.getElementById("xxx_div").style.display = "block";
    unloading = true;
};