jQueryUI dialog close button invisible

jQueryUI dialog close button invisible

Hi guys

Like the subject line says, I have a dialog where the "x" icon is not visible.  If I mouseover the toolbar, I can make the button appear, but the "x" does not appear even then.

NOTE - it's not "my code" - the same is happening with the demos here - no "x" icon.

Firefox 4 on Vista Ultimate SP2.

R