function setOverlayHeight() {
		overlayDiv = document.getElementById('overlay');
	
		// Calculate page height
		var docHeight;
		if (window.innerHeight && window.scrollMaxY) {// Firefox
			docHeight = window.innerHeight + window.scrollMaxY;
		} else if (document.body.scrollHeight > document.body.offsetHeight){ // all but Explorer Mac
			docHeight = document.body.scrollHeight;
		} else { // works in Explorer 6 Strict, Mozilla (not FF) and Safari
			docHeight = document.body.offsetHeight;	
	 	}
	 	
	 	overlayDiv.style.cssText = 'height:'+docHeight+'px;';
 	}