In firefox e chrome è possibile.

codice:
<script>
function get_info_img(what)
{
var file = document.getElementById('ilmiofile');
var info_file = file.files[0];

if (what=='size')
alert(info_file.size);
else
alert(info_file.value);
}
</script>

<input id="ilmiofile" type="file" onchange="get_info_img('size');" />