As an update to this, Firefox RC1/2 run the html nicely.
However I noticed a slight anomaly under the circumstances. The ling string in the mark read url can potentially break the tables so I created a simple phrase to put things back into order.
(I have also been thinking of adding this as an icon instead of text to keep things cleaner.)
In any case it's a great hack, very useful to have. - thx
Code:
<if condition="$show['forumlink']">
<td class="alt1"><a href="forumdisplay.php?$session[sessionurl]f=$thread[forumid]">$thread[forumtitle]</a><br><if condition="$display['getnew']">$vbphrase[mark_forum_read]</if></td></if>