When you use the xslt parameter of the api. it inserts a line of the form:
<?xml-stylesheet href="/w/index.php?title=MediaWiki:extractFirst.xsl&action=raw" type="text/xml" ?>
This should be
<?xml-stylesheet href="/w/index.php?title=MediaWiki:extractFirst.xsl&action=raw" type="text/xsl" ?>
As all browsers recognize text/xsl (despite it being technically "non-standard"), well text/xml is not recognized by internet explorer. See [[w:Xslt#XSLT_media_types]].
Cheers,
Bawolff
Version: 1.16.x
Severity: minor
URL: http://en.wiktionary.org/w/api.php?action=parse&prop=text&page=word&format=xml&lang=en&xslt=MediaWiki:extractFirst.xsl