Problem with namespace and server-side XSLT

I'm using PHP with the DOM and XSL extensions to generate XHTML 
documents (I had also met this problem with PHP4/DOM XML/XSLT). 
Everything is going pretty like I want, except when it comes to the 
default namespace of the "html" tag.
This namespace doesn't require a prefix (as it is a "default" namespace) 
but if I doesn't specify one, the processor uses a generic one (ns1).
This is not a big issue, but I'd like to know if it's possible to avoid 
that, except by using <xsl:attribute 
name="xmlns">[namespace]</xsl:attribute>.
The main problem is more or less coming from Firefox, as it apparently 
has a problem with XHTML served as application/xhtml+xml with a prefix 
for the html element.

Thanks,
Georges Discry