I\'m not sure whether this bug applies to Firefox only or also to WebKit-based browsers, but it\'s really, really annoying.
I\'ve got a template/framework for my CMS in
You can use the spread radius (the 4th length) to make the shadow's size smaller than the element's size and then a large y offset to let it show beneath the element. Something like box-shadow: 0 10px 10px -5px black;
(of course I don't know what values you need since you didn't provide a fiddle, you need to play around with them in the dev tools). Keep in mind that the spread radius causes the shadow to expand/contract from all sides. So, for example, a spread radius of -1px will actually make the shadow 2px narrower.