position fixed

[Karl]

Moin,
warum bricht im FF die Tabellenstruktur auseinander?

<table border="1">
 <tr style="position:fixed; background-color:#CCCCCC">
  <th>td1</th>
  <th>td2</th>
  <th>td3</th>
  <th>td4</th>
  <th>td5</th>
 </tr>
 <tr>
  <td>td1td1td1td1</td>
  <td>td2</td>
  <td>td3</td>
  <td>td4</td>
  <td>td5</td>
 </tr>
 <tr>
  <td>td1td1td1td1</td>
  <td>td2</td>
  <td>td3</td>
  <td>td4</td>
  <td>td5</td>
 </tr>
</table>