Iframe Resizing On Opera

the problem is, i have this javascript code in my aspx page that i want
it to work on almost all browsers, especially opera and safari :

function resize(){
displayFrm = document.getElementById("ifrmDisplay");

innerDoc = (displayFrame.contentDocument) ?displayFrm.contentDocument :
displayFrm.contentWindow.document;

objToResize = (displayFrm.style) ? displayFrm.style : displayFrm;

objToResize.height = innerDoc.body.scrollHeight;
}

the code above gets called every time a new page is loaded inside the
iframe (ifrmDisplay) what its doing is resizing the iframe so it can
have the same size as the page inside it, so i can eliminate the need
for vertical scroller for the iframe, i assumed that it works on opera
and IE at the same time, when i tried it out, it worked on IE but not on
opera. after lot of time in researching how i can get workaround this
issue with opera, that is the best possible solution i have and yet it
doesnt work. so i gave up and asking you if you can help me out here ,
coz this is jst driving me crazy!

the problem is im not a javascript expert, to be honest i jst started
doing javascripts about two days ago, that is why im in need for help

by the way, here is inner html for the iframe if its any use

<iframe id="ifrmDisplay" style="Z-INDEX: 99; LEFT: 187px; WIDTH: 567px;
POSITION: absolute; TOP: 136px; HEIGHT: 408px" src="" scrolling="no"

</iframe>