This is driving me nuts. I've tried everything I can think of. I'm modifying a theme Painted Desert 1 by JTk - http://www.jtkconsulting.com.
Background image will only repeat for the height of the sidebar menus in Firefox, but works fine in IE.
See http://gnfoster.com/WordPress for what I mean. If the entries aren't there, click on Become a Christian in the menu... It's a page with lots of text.