Here it is the most minimal code that still highlights the Firefox behavior (In Chrome and IE the scrollbar is shown as expected)
<html>
<body>
<table style="width:100%; height:100%;">
<tbody>
<tr>
<td style=" width: 75%; height: 100%; vertical-align: top; background-color: #FFE4C4;">
<div style=" width: 100%; height: 100%; overflow: auto;">
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
<div> 1 __________________ line </div>
</div>
</td>
<td style="background-color: #DEB887;"> <div> . </div> </td>
</tr>
</tbody>
</table>
</body>
</html>
Any hint to have it working even in FF ? Many Thanks