A second XMLHttpRequest gives NS_ERROR_FAILURE
<p>with JavaScript I request a File with XMLHttpRequest and it works. But when i want to request a file (no matter if it is the same or not) the second time, I get a NS_ERROR_FAILURE at the line with req.open...</p>

<pre><code>function readfile(file) {
  var req = new XMLHttpRequest();
  alert(file);
  req.open('GET', file, false);
  req.send();
  return req.responseText;
}
</code></pre>

<p>The files are in the same folder.
1-2 months ago (with an older Firefox) it worked, but now (with Firefox 14) I get this error.</p>
