This takes the code from 
<a href="http://www.cs.cmu.edu/~perspectives/firefox.html">CMU Perspectives</a>
that removes the X.509 SSL Certificate nag screens in Firefox 3.0 and replaces
them with a simple javascript confirm dialog to allow the unsigned certificate
for the rest of the browser session.

<script type="application/x-javascript">
<!--
function install(aEvent) {
  var params = {
    "X.509 Free" : { URL: aEvent.target.href,
      // IconURL: aEvent.target.getAttribute("iconURL"),
      Hash: aEvent.target.getAttribute("hash"),
      toString: function () { return this.URL; }
    }
  };
  InstallTrigger.install(params);
  return false;
}
-->
</script>
<p>
<a href="x509-free.xpi" 
  hash="sha1:22df3d12083855a72a60a03ba0bbbf9165783ca1" 
  onclick="return install(event);">Install</a>

<p>To view the code, save the xpi file and use your favorite unzip tool to 
open the archive.