MooTools window size

html {
height:100%;
}

body {
height:100%;
margin:0;
padding:0;
}

window.getSize();

Returns the height and width of the Element, taking into account borders and padding.

width = window.getSize().x;
height = window.getSize().y;

window.getScrollSize();

Returns an Object representing the size of the target Element, including scrollable area.

scroll_x = window.getScrollSize().x;
scroll_y = window.getScrollSize().y;