Background attachment set to fixed not FF friendly

Check this site: http://cafedietrichs.com/

In Chrome and Safari, the background attachment does as I want, however, in Firefox, the background height is apparently fixed to the viewport height. Notice how, when you scroll, the background only shows through up to the height of the viewport.

What do I need to do to make FF happy? Here’s the relevant CSS.

html:before{
content:’ ';
display:block;
position:absolute;
z-index:-1;
top:0;
left:0;
right:0;
bottom:0;
background:url(http://cafedietrichs.com/wp-content/themes/ce4/styles/chicago-alt2/background.png) repeat fixed !important;
}