Iframe over Grid

I have an Iframe which needs to come up when a button is clicked.
However the grid in the page displays over the Iframe which opens up.
I am at a loss what did i do wrong?

I changed the Zindex of the css in the grid from 1000 to 500 and 10000 ro 600.

Also changed the iframe ZIndex to 700.
Everythign works fine in IE now but in firefox the grid still displays over the Iframe.
What am I doing wrong here ?

if the grid and the iframe are not inside the same parent element - then zindex of the parents defines which element is on top. I think this behavior is actually different between different versions of IE and FF.

Would that be the zIndex of the straight parentNode of both the components or the Nodes which are siblings of each other in the hierrarchy finally?

That is parentNode.parentNode.parentNode?

This is different in different browsers - some ignore the dom hierarchy and only use element zIndex, but others use only siblings zIndex to calculate which one is above.