Firefox ignores absolute positioning in table cells

I am trying to absolutely position an element inside a table cell. The TD has position:relative and the element has position:absolute.

This works great in all browsers except in Firefox where it is positioned relative to an ancestor relative container.

You can see this reproduced in this fiddle: http://jsfiddle.net/ac5CR/1/

Does anyone know if I miss some CSS setting that can fix that in Firefox?