EDIT: as this problem is now "solved" to the point of working, I am looking to have the information on why. For the fix, see my comment below.

I have an web application which repeatedly downloads wav files dynamically (after a timeout or as instructed by the user) into an iframe in order to trigger the a default audio player to play them. The application targets only FF 2 or 3. In order to determine when the file is downloaded completely, I am hoping to use the window.onload handler for the iframe. Based on this stackoverflow.com answer I am creating a new iframe each time. As long as firebug is enabled on the browser using the application, everything works great. Without firebug, the onload never fires. The version of firebug is 1.3.1, while I've tested Firefox 2.0.0.19 and 3.0.7. Any ideas how I can get the onload from the iframe to reliably trigger when the wav file has downloaded? Or is there another way to signal the completion of the download? Here's the pertinent code:

HTML (hidden's only attribute is display:none;):

<div id="audioContainer" class="hidden">
</div>

JavaScript (could also use jQuery, but innerHTML is faster than html() from what I've read):

waitingForFile = true; // (declared at the beginning of closure)
$("#loading").removeClass("hidden");
var content = "<iframe id='audioPlayer' name='audioPlayer' src='" +
    /path/to/file.wav + "' onload='notifyLoaded()'></iframe>";
document.getElementById("audioContainer").innerHTML = content;

And the content of notifyLoaded:

function notifyLoaded() {
    waitingForFile = false; // (declared at beginning of the closure)
    $("#loading").addClass("hidden");
 }

I have also tried creating the iframe via document.createElement, but I found the same behavior. The onload triggered each time with firebug enabled and never without it.

EDIT: Fixed the information on how the iframe is being declared and added the callback function code. No, no console.log calls here.