Onclick in anchor tag fails in Firefox

In the two table cells, below, there are anchor tags.

The first table cell works, the second breaks the browser and displays nothing.

In the first table cell, which works, the anchor tags just contain a reference to "href".

In the second table cell the anchor tag contain an "onclick" event, and this just displays a blank page (failing silently).

I was just wondering why?


This table cell works:

<td>
<div style="position: relative;">
<div style="position: relative; color: Black; z-index: 5;">
<nobr>  <a href="#RSL5T0CI1">The Civil War</a>  </nobr>
</div>
<div style="position: absolute; top: 0px; left: 0px; width: 100%; height: 100%; background-color: #DA70D6; z-index: 1; -ms-filter: \'progid:DXImageTransform.Microsoft.Alpha(Opacity=20)\'; filter: alpha(opacity=20); opacity: 0.2;">
</div>
</div>
</td>


And this table cell dosent work:

<td>
<div style="position: relative;">
<div style="position: relative; color: Black; z-index: 5;">
<nobr> 
<a onclick="showCustomer('tl=TEOI81A2X&id=AAAA71GG1&todo=gotocenter','void')" href="#AAA5S0CI1">
The Civil War</a>  </nobr></div>
<div style="position: absolute; top: 0px; left: 0px; width: 100%; height: 100%; background-color: #DA70D6; z-index: 1; -ms-filter: \'progid:DXImageTransform.Microsoft.Alpha(Opacity=20)\'; filter: alpha(opacity=20); opacity: 0.2;">
</div>
</div>
</td>