I've upgraded to FireFox 4 recently and suddenly one of my flash modules stopped working. This a copy/paste of the object structure from firebug (double dots are there for simplicity):
<object width="100%" height="100%" type="application/x-shockwave-flash" data=".." name="..">
<param name="flashvars" value="..">
<param name="wmode" value="obaque">
<param name="allowscriptaccess" value="always">
</object>
Now... what's that obaque value on wmode param?.. It was meant to be "transparent" actually, at least that's what I had in my embed code.