javascript not waiting for function return

function fade_about_out() {
	document.getElementById('about').style.MozOpacity -= .1;
	if(document.getElementById('about').style.MozOpaci  ty < .1)
	{
		document.getElementById('about').style.display='no  ne';
		return;
	}
	setTimeout(fade_about_out, 20);	
}
function fade_design_in() {
	document.getElementById('design').style.MozOpacity   += .1;
	if(document.getElementById('design').style.MozOpac  ity > 1)
	{
		
		return;
	}
	setTimeout(fade_design_in, 20);	
}

function show_design() {
	//hide about
	document.getElementById('about').style.MozOpacity = 1;
	fade_about_out();
	//show design
	document.getElementById('design').style.MozOpacity   = 0;
	document.getElementById('design').style.display=''  ;
	fade_design_in();
}