Hi,
Can you try this in the dialog code ?
<script>
alert(window.XMLHttpRequest);
alert(window.ActiveXObject);
</script>
if you get "ActiveXObject is not defined" , that means XMLHttpRequest is not available.
And in the uploader , there's one line check the window.ActiveXObject
Maybe your dialog have js library simulating the ActiveXObject function
What's the firefox version?
Regards,
Terry