How do I fix a blinking dropdown menu when it overlaps div in SharePoint?

Question

I am opening a pdf in an div object in a Content Editor Web Part. Some parts of my dropdown menu overlap the div and causes the menu to "blink" (hides under the pdf then shows on top) as you scroll over it.

I am using IE6 and I was able to try this page in Chrome, and the menu gets hidden behind the pdf div. Is there any way to fix this blinking and hiding in SharePoint Designer or in a Content Editor Web Part? (I tried changing the AspMenu in the master page's z-index to 1000) If no way exists, should I try to move the div away from the menu?

My code for the pdf is:

  <div style="z-index:-1">
  <object data="page.pdf" 
     type="application/pdf" width="100%" height="900"></object>
 </div>