<html>
<body>
<table>
<tr>
<td colspan = "2">hello</td>
</tr>
</table>
</body>
</html>
it gets confused with the space next to the colspan, and displays it as:
<html>
<body>
<table>
<tr>
<td colspan =" 2">hello</td>
</tr>
</table>
</body>
</html>
which to any perfectionist programmer could be quite an annoyance. Especially if that section of the page is being dynamically generated by a PHP script, and they waste many minutes trying to track a fault in their code when it turns out to be a browser quirk...
Update 12 Sep 2005: This is fixed in Firefox 1.5 beta 1.