I'm using a "frame" layout similar to the one in this excellent answer: a div #top at the top of the page, a div#left on the left, and a div #main with the main content. The #top and #left divs contain navigation menus.

Now I want to use a popup div using the AjaxControlToolkit ModalPopupExtender inside the content (#main) div.

This works fine on IE8 (where #top, #left, #main all have position:fixed), but when I run it on IE6, the modal background only covers the #main div - I need it to cover the whole of the page including the #top and #left navigation divs.

Looking at the script for ModalPopupExtender, it appears to be searching up the parent hierarchy until it finds a parent with position relative or absolute. And in the IE6 rendering, the #main div has position:absolute because position:fixed is not supported, which I guess explains what is happening.

Any suggestions for the best/easiest way to get this working properly on IE6? Ideally without modifying the ModalPopupExtender code, but I'll do this if I have to and it's the best solution.