Google Conversions Not Working - Script Won't Load

I have an AdWords campaign for which I have set up conversion tracking. Google generated some code which I placed after the the begin body tag:

  <!-- Google Code for Sign Up Conversion Page -->
<script type="text/javascript">
    /* <![CDATA[ */
    var google_conversion_id = 999999999;
    var google_conversion_language = "en";
    var google_conversion_format = "3";
    var google_conversion_color = "ffffff";
    var google_conversion_label = "redacted";
    var google_conversion_value = 0;
    /* ]]> */
</script>
<script type="text/javascript" src="http://www.googleadservices.com/pagead/conversion.js"></script>
<noscript>
    <div style="display:inline;">
        <img height="1" width="1" style="border-style:none;" alt="" src="http://www.googleadservices.com/pagead/conversion/999999999/?label=redacted&amp;guid=ON&amp;script=0"/>
    </div>
</noscript>

It seems to work in Safari and IE. But it in Firefox and Chrome, loading conversion.js fails. In Firefox the status says aborted, in Chrome failed. No status code.

I've tried putting this code in various places including head and at the bottom.

Ideas?

Do you have Adblock Plus or similar ad-blocking software installed? Adblock Plus will block the download of conversion.js, so you will need to disable ad-blocking on your site for testing.