Using CSS generated pseudo elements and generated content to display a triangle in a th element. See the test case here http://jsfiddle.net/GvDzr/1/ Both Foo and Bar should have a black triangle underneath them. The exact same style rules are applied to a div and a th. The desired effect is achieved on the div but not on the th. This works as expected in webkit and opera but not in firefox.

This has nothing to do with generated content; you get the same thing if you just use a <span>.