border bottom not working print preview firefox css

I have a table in my webpage. When i view the page in print preview in firefox the border bottom of the td doesn't display sometimes. In other browsers it's working fine. How to fix this?

Html:

<table width="100%" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td>Heading 1</td>
    <td>Heading 1</td>
    <td>Heading 1</td>
  </tr>
</table>

css:

table td{ border-bottom:1px solid #000;}