Toggling of iFrame working fine in Firefox but not in IE

Toggling of iFrame working fine in Firefox but not in IE

I have different iFrames on my page and one of the iFrame has pdf plugin that shows the PDF document and i have another iFrame that pops up on delete button click and  a function to toggle the iFrames. It works fine in Firefox but in IE my pop up iFrame is always behind the PDF.
Any thought how can I set it right, there is some issue with the z-index of PDF, it is set to infinity something like that in IE !

Thanks.