The following formula should be the fraction 5/3 as MathML: $\frac{5}{3}$

However, when doing the transformation in Firefox by loading the XML file xslt-html5-math.xml the MathML tags get interpreted as undefined HTML tags.

This is generated from xslt-html5-math.xml using xslt-html5-math.xsl either by Firefox when loading it, or by xsltproc with:

xsltproc -o index.html xslt-html5-math.xsl xslt-html5-math.xml