var mPopUpLeft, mPopUpTop;
mPopUpLeft = (screen.availWidth - 900) / 2;
mPopUpTop = (screen.availHeight - 760) / 2;

function fnDonate() {
    window.open('Donate.htm', 'null', 'left=0,top=0,width=900,height=760,toolbar=0,resizable=0,titlebar=0,top=' + mPopUpTop + ',left=' + mPopUpLeft);
}