You left out which browser versions you are testing. For example, the flash displays behind all other elements in Safari 4.1. Since Chrome uses the same layout engine, you're probably using an old version of Safari, and it's probably related to the z-index. Set the z-index to all elements other than the BG to a positive value. You could create a FG element that contains all the other foreground elements to make styling simpler.
HTML Code:
<body>
<div id="BG">...</div>
<div id="FG">...</div>
</body>
Also try a web search for "Safari flash z-index". Remember, Google is your friend.