EXTRA_EXPORTED_RUNTIME_METHODS missing
unless this patch is applied:
sed -e "s/-o fastXmlLint.js/-s EXTRA_EXPORTED_RUNTIME_METHODS='[\"ccall\", \"cwrap\"]' -o fastXmlLint.js/g" -i Makefile.emEnv
firefox will show up the webpage but the javascript execution will fail and xmlmirror won't be working at all and look broken.