I haveing the problem that the hover is not working in Firefox! It is working in Chrome, IE 9, IE 8 and IE 7. Does somewone know this problem and how to fix it?
It looks like the hover event isn't getting fed down to the span.
Try selecting button:hover span instead of button span:hover
button:hover span
button span:hover
Here's a JSFiddle that works okay by doing the above: http://jsfiddle.net/3j7G5/