We had a long-standing problem whereby the Superfish drop-down menus wouldn't expand on Internet Explorer 8. After much Googling over many months, I finally stumbled on the root cause: a proprietary CSS directive, -ms-filter, screws up the Z‑index logic, causing the menu items to be rendered "beneath" the rest of the page content. (Yet another reason why yours truly detests Microsoft.)
Simply commenting out the -ms-filter directive in $D7/sites/www.iac.org/themes/iac/css/local.css cured the issue.
