How to overlay flash on WMP in FF?

Hi, I used to use "CSS Layer" to put a semi-transparent flash over
Windows Media Player in a html. such like :
<style>
#Layer1
....
#Layer2
....
</sytle>


<div id="Layer1">
<!-- embed a WMP here-->
</div>
<div id="Layer2">
<!-- embed a semi-tranparent flash here-->
</div>


it works well on IE, but in FF, it didn't. I also did some other tests,

when in FF, I can use similiar syntax to overlay TEXT on Flash,
flash on TEXT,
but I couldn't overlay anything on WMP. even TEXT.


Does someone know the matter?Thanks!