[danik.js]

<tr id="24" class="edit_tr">
<td>24</td>
<td>
<input name="firstfield" class="editbox_input" type="text" value="">
</td>
<td style="display:none;">
<input name="secondfield" class="table_ajax" type="text" value="04_13">
</td>
<td style="display:none;">
<input name="thirdfield" class="table_ajax" type="text" value="Иван Иванович">
</td>
<script>
$(.edit_tr).change(function(e){
    var $firstfield = $(this).find('input[name="firstfield"]'); 
    var $secondfield = $(this).find('input[name="secondfield"]'); 
    var $thirdfield = $(this).find('input[name="thirdfield"]');
    e.target; // поле, породившее событие change
});
</script>