simple javascript question

hi folx -

just a very simple question: i'm using a few lines of javascript to replace a scrollbar in an iframe. this code is in my static html parent window:

<script>
  
  var staticscrollspeed=3 //Enter scroll speed in integer (Advised: 1-3)
  
  var xcurrentscrollspeed=0
  var ycurrentscrollspeed=0
  
  
  function scroll(){
    window.frames[0].window.scrollBy(xcurrentscrollspeed,ycurrentscrollspeed)
  }
  
  setInterval("scroll()",20)
  
  </script>
<div id="jsscroll">
  <a onmouseover="ycurrentscrollspeed=-staticscrollspeed" onmouseout="ycurrentscrollspeed=0"><img src="assets/up.gif" /></a><br />
  <a onmouseover="ycurrentscrollspeed=staticscrollspeed" onmouseout="ycurrentscrollspeed=0"><img src="assets/down.gif" /></a>
  </div>

i'm having trouble diagnosing why it works fine to scroll other static html pages, but won't scroll drupal pages loaded into the iframe in firefox (works in safari). i've chopped my zen page.tpl.php to bare bones, eliminating any reference to strict xhtml, and not loading any other javascript files, but still can't get it to scroll. any ideas? thanks in advance.

peace,
-ryan