Why does Firefox not render border of table with empty tbody?

Question

Firefox does not render table cell borders correctly when a table has an empty tbody.

But if you use the pseudo selector tbody:empty {display:none;} to hide the tbody element, everything is rendered as expected.

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>

Answer 1

It most likely belongs to Bug 409254 and Bug 217769 on Firefox.

Side note: Although an empty tbody is valid in HTML 5, but the number of the cells in each row group should be matched (except using colspan) in one table.

A workaround would be drawing the borders separately on both the table and cell elements.

table {
    border-collapse: separate; /*changed from collapse*/
    border-spacing: 0;
    border: 1px solid;
    border-width: 0 0 1px 1px; /*draw bottom and left borders*/
}
th,
td {
    border: 1px solid;
    border-width: 1px 1px 0 0; /*draw top and right borders*/
}

jsfiddle