Background image not displaying in Firefox

I’m in the process of getting the self-hosted wordpress styled for our new site. And I notice that in Firefox, the background image doesn’t show up but it does in other browsers. Normally, it’s a size issue when this happens but I’m not familiar with php so I’m a little lost on how to resolve this issue. I don’t have the size specified in the css. Can anyone take a look at it for me?

http://www.radiantbylori.com/radiantblog/

Thanks!