This is the result of validating the HTML of a random bug page:

Error Line 344, Column 85: there is no attribute "SPELLCHECK" 
…  value="build fails on 'make' #1" size="80" maxlength="255" spellcheck="true">

Error Line 503, Column 11: invalid comment declaration: found name start character outside comment but inside comment declaration 
          initHidingOptionsForIE('rep_platform');
Info Line 483, Column 1: comment declaration started here 
<!--

Error Line 503, Column 12: character data is not allowed here 
          initHidingOptionsForIE('rep_platform');

Error Line 506, Column 17: end tag for element "SCRIPT" which is not open 
        </script>

Error Line 509, Column 17: document type does not allow element "SELECT" here 
                >

Error Line 517, Column 39: document type does not allow element "SCRIPT" here 
        <script type="text/javascript">

Error Line 523, Column 38: document type does not allow element "SCRIPT" here 
       <script type="text/javascript">

Error Line 526, Column 11: end tag for "TABLE" omitted, but its declaration does not permit this 
      </td>
Info Line 357, Column 9: start tag was here 
        <table>

Error Line 528, Column 1: character data is not allowed here 
-->

Error Line 720, Column 11: end tag for element "TD" which is not open 
      </td>

Error Line 721, Column 10: document type does not allow element "TD" here 
      <td>

Error Line 725, Column 63: document type does not allow element "TD" here 
      <td id="bz_show_bug_column_2" class="bz_show_bug_column">

Error Line 869, Column 9: end tag for element "TR" which is not open 
    </tr>

Error Line 870, Column 8: document type does not allow element "TR" here 
    <tr>

Error Line 875, Column 10: end tag for element "TABLE" which is not open 
  </table>

Warning Line 590, Column 23: reference to non-existent ID "TARGET_MILESTONE" 
          <label for="target_milestone">