I've had this issue since Firefox 3 has been released, and just got around to trying to fix it now.
It appears that FF3 is removing the background attribute from the CSS when loaded.
Offending Site is here: http://www.surpassarcade.com/
You will notice the difference right away when loading in IE.
This is the code in the CSS file:
But when FF3 loads it, it produces:
background: #4e8333 url('../images/container_bg.jpg') top repeat-x left;
text-align: center; /* for IE */
(obtained via Firebug)
Has anyone else had this problem or know why its occurring?