XSLT/XPATH problem, possible bug

Hi,

I have this weird problem with Firefox and xslt transformations. The xslt
transformation takes place and I get no errors, but some aspects of the
transformations related to xpath fails. It may not be a problem with the
xslt processing at all, and I can't really locate the problem.

The website works like this:

based on a url argument, e.g. xmlserializer.php?action=upcomingconcerts, an
xml file is serialized serverside from a mysql database. The xsl stylesheet
link in this output is then configured to call xslserializer.php with the
same argument, which will return the according stylesheet. It all works very
well, and everything validates, but when I set up additional arguments for
sorting/filtering the transformation, nothing happens. The arguments work
their way into the output and all, but it is like Firefox ignores parts of
the select statements in the xsl output.

AFAIK Its not a problem related to wrong namespaces, dtd mistakes or
anything. I'll appreciate any help, even the smallest comment about awful
formatting of the xml/xsl/dtd output of the php scripts ; - )

The website works fine in Opera 9 beta and IE.

Here's the address for the xml output (mainpage):
http://studenterkonto.humaniora.sdu.dk/labjo05/webstandarder/xmlserializer.php?action=upcomingconcerts

you can see the related xsl stylesheet here:
http://studenterkonto.humaniora.sdu.dk/labjo05/webstandarder/xslserializer.php?action=upcomingconcerts

and the DTD here:
http://studenterkonto.humaniora.sdu.dk/labjo05/webstandarder/dtd.php

TIA,

Michael Hansen

Btw,

Maybe I should make it clear that I don't perform the transformation in 
javascript, I let FireFox handle it all.