It seems that on the Mac OSX (firefox 2.0), when trying to layer DOM elements
on top of flash using wmode=opaque (or transparent) and setting the z-index,
that if an element is completely contained inside of the flash, it will display
beneath the flash animation.

Nick Cowie has also observed this, but decided it was "random" whether the
layer would be shown above or below the flash.
http://nickcowie.com/2006/layering-flash-and-html-tutorial/

He indicates that an iframe shim might be a possible workaround, but from my
experiments and iframe shim doesn't help at all.

Anybody had any luck getting around this?

Just to add to what Chris is saying, in my experience: if you try to layer HTML
elements above or below flash using wmode =opaque or transparent and you view
the site using a Mac or *nix flash player the HTML may appear above the Flash,
no matter what the z-index or source order.

It only happens with Mac or *nix machines and not Windows.

If you want to see this in action and are using a Mac or other *nix box go to
my blog http://nickcowie.com and scroll down to the footer, then scroll up and
back down again, the HTML footer will appear in front of the flash background
50% of the time and the other 50% of the time the flash background will appear
in front of the HTML