<xsl:template match="comment()">
                 <xsl:variable name="commentFootnoteId"
select="substring-before(substring-after(., '&quot;'), '&quot;')" />
                 <xsl:copy-of select="/chapter/footnote[@id = 
$commentFootnoteId]" />
   </xsl:template>


Perfect. I started using keys but this one seems to be more clean.

Thanks Mukul.

Best,
Pankaj