Firefox Onmousedown Popup/layer Focus/blur

I'm trying to create a control which when the mouse button gets
pressed on one div an absolute positioned div pops up in
place of the cursor. From there the cursor should interact with
the dialog before the mouse button is released. In other words
one element will catch onmousedown, display the popup, and
the popup element will catch onmouseup. This works fine in
IE as the popup automatically accepts following events,
but my problem is in Firefox.

In Firefox everything behind the popup
still receive events even though they can't be seen
(hidden by the popup). I have to release the mouse button and then
click on the popup again before it accepts the onmouseup event.

I also used a different cursor on the popup to see if Firefox
recognized it was there at all. Still the cursor doesn't change
until I release themouse button and move the cursor across
the popup element.

I've tried focus/blur, timeout delays, hiding the first element
(the one which receives onmousedown) but nothing works.

The only thing that works is hiding the entire body and then
using setTimeout to show the entire body again 1ms later.
Obviously though that is very ugly.