if( document.cookie.indexOf( 'popup=hide' ) < 0 ) {
window.open( './popup.html', 'Popup window', 'width=300,height=150' );
var tomorrow = new Date();
tomorrow.setDate( tomorrow.getDate() + 1 );
document.cookie = 'popup=hide;expires=' + tomorrow.toGMTString() + ';path=/';
}