Reader: fix overflow display bug on Firefox

[designsimply]

Steps to reproduce:

1. Publish a new post including a table with images in two 50% width colums
2. View the post in the Reader

Result: the table is not constrained to the content area when the post is viewed in the Reader using Firefox.

^{Seen at https://wordpress.com/read/post/feed/38371659/875724951 using Firefox 42.0 on Mac OS X 10.10.5}

Example HTML

<table>
<tbody>
<tr>
<td valign="top" width="50%">
<h4>Control
<a href="https://design5279.files.wordpress.com/2015/11/img_0860.jpg"><img class="alignnone wp-image-9709 size-large" src="https://design5279.files.wordpress.com/2015/11/img_0860.jpg?w=660" alt="gapps-control" width="660" height="62" /></a></h4>
</td>
<td valign="top" width="50%">
<h4>Variation <a href="https://design5279.files.wordpress.com/2015/11/img_4652.jpg"><img class="alignnone wp-image-9716 size-large" src="https://design5279.files.wordpress.com/2015/11/img_4652.jpg?w=660" alt="gapps-variation" width="660" height="68" /></a></h4>
</td>
</tr>
</tbody>
</table>

/hat tip @stephanethomas for the original report

[alexjgustafson]

Looks like this is fixed from the Mozilla end, but won't be available to users until Firefox 46. (#).

FF46 is due out in April. (#)

Viewing in Firefox Developer Edition, the problem is gone:

[lancewillett]

Closing as noted above, resolved in newer Firefox versions.