Popup Windows: left & top

left and top set the position of the popup on the screen. If you don't put left and top the browser puts the popup where it wants. For example, this command in the popup script puts the popup left from the left of the screen and top from the top:

window.open(href, windowname, 'width=250,height=150,left=50,top=100,scrollbars=yes');

gives us this popup: this popup.