I was able to get this into a working state by using background-size:cover
#wrapperbg{
position: relative;
top: 0;
left: 0;
width: 100%;
overflow: hidden;
-moz-background-size: cover;
background-size: cover;
margin: 0;
padding: 0;
background-image: url('../images/animation/spritechap.jpg');
}