If Firefox isn't displaying table cell borders correctly in the presence of an empty tbody, a simple solution is to use the pseudo selector tbody:empty {display:none;} to hide the empty tbody element. This will ensure that everything is rendered as expected.
For a demonstration and code examples, check out this jsfiddle
table {
border-collapse: collapse;
}
th,
td {
border: 1px solid #000;
}
.fixed tbody:empty {
display: none;
}<table class="broken">
<thead>
<tr>
<th>1</th>
<td>2</td>
<td>3</td>
</tr>
</thead>
<tbody></tbody>
<tfoot>
<tr>
<th>1</th>
<td>2</td>
<td>3</td>
</tr>
</tfoot>
</table>
<hr />
<table class="fixed">
<thead>
<tr>
<th>1</th>
<td>2</td>
<td>3</td>
</tr>
</thead>
<tbody></tbody>
<tfoot>
<tr>
<th>1</th>
<td>2</td>
<td>3</td>
</tr>
</tfoot>
</table>