I know this is probably not silverstripe specific, but anyhow,
I am using the superfish dropdown menu with silverstripe , and I have a flash banner-slideshow on the home page,
In firefox everything works great, however in safari (win) and ie the dropdown menu goes behind the flash banner,
I initially had to remove the rounded corners in the css of the dropdown portion to get it going on top in firefox.
I used this great silverstripe tutorial to incorporate flashcontent (including alt content for ipads etc.) http://www.ssbits.com/embed-flash-content-using-swfobject/
and,,, what else, I have a high z-index for the flash as well as a higher z-index for the menu. the menu gets read in before the flash gets read in.
The flash slideshow sits ontop of a slideshow-background-image (which the dropdown goes on top of fine, just the flash portion that is the problem).
I also tried this - setting position relative for the containing divs; : http://webdemar.com/webdesign/superfish-jquery-menu-ie-z-index-bug/
would be great if anyone has had the same problems and knew whats missing, and when I get better at silverstripe hopefully I can pay it back and help someone else out.
and thanks for silverstripe!