I've been using FF3 for a while now so I didn't notice this issue but as soon as I loaded FF2 it was obvious.   Firefox has issues when you dynamicly load flash through SWF object on a Mac.  In FF2 with a Mac all you'll see is a white box that requires you to click on it... then everything will look correct. If you don't want your users to have to click a flash object just to have the page look the way you intended then try the code below.

To fix it you just need to force a quick little behind the scenes redraw in javascript:

swfobject.addLoadEvent(forceRedraw);

function forceRedraw() {
document.getElementById("yourflashobjectidhere").style.display = "block";
}

Solution by  bobbyvandersluis at http://code.google.com/p/swfobject/issues/detail?id=53&can=1 comment #7