-text_field_with_auto_complete- browser problems

Hello,
i'm using the following in my rails app. works like a charm on IE.
but on FF no autocomplete popup is displayed. can somebody help?

rails code:
  <p>
     <%= text_field_with_auto_complete :person, :nachname, {},
     {
      :select => 'name',
      :after_update_element =>
        "function(element,value) " +
        "{ " +
        remote_function(:update=>'Kundendaten',
          :url=>{:action=>:update_kundendaten},
          :with=>"'adr_id='+value.id") + ";" +
        "}"
     }
     %>
  </p>

html result:
<p>
    <style>
      div.auto_complete {
              width: 350px;
              background: #fff;
            }
       div.auto_complete ul {
              border:1px solid #888;
              margin:0;
              padding:0;
              width:100%;
              list-style-type:none;
            }
      div.auto_complete ul li {
              margin:0;
              padding:3px;
            }
      div.auto_complete ul li.selected {
              background-color: #ffb;
            }
      div.auto_complete ul strong.highlight {
              color: #800;
              margin:0;
              padding:0;
            }
</style>

<input id="person_nachname" name="person[nachname]" size="30"
type="text" />
<div class="auto_complete" id="person_nachname_auto_complete"></div>

<script type="text/javascript">
//<![CDATA[
var person_nachname_auto_completer = new
Ajax.Autocompleter('person_nachname', 'person_nachname_auto_complete',
'/vermietung/auto_complete_for_person_nachname',
{afterUpdateElement:function(element,value) { new
Ajax.Updater('Kundendaten', '/vermietung/update_kundendaten',
{asynchronous:true, evalScripts:true,
parameters:'adr_id='+value.id});}, select:'name'})
//]]>
</script>
</p>