Out-of-Stock Product Combinations Show in Chrome and Safari, not in Firefox

[intandem]

Please see link to a sample product in a development shop:

 

http://www.d1160766-...troller=product

 

In Chrome and Safari (on Mac), the full list of sizes displays in the drop-down even though only a few of them have a quantity set up.

 

In Firefox however, the limited list displays correctly.

 

Any ideas what might be causing this? Can't let this shop go live otherwise

 

I have Attribute Wizard Pro installed by the way.

 

Thanks in advance for any help!

Edited April 25, 2013 by intandem (see edit history)