application/vnd.mozilla.xul+xml is defined twice in freedesktop.org.xml.in: $ sed -nre 's,^.*mime-type type="(.*)".*$,\1,p' freedesktop.org.xml.in | sort | uniq --repeated --count 2 application/vnd.mozilla.xul+xml The duplicate definition was added in commit 15094b2e382937bbe9668b6acf4c35d680d008d6 .
Fixed in master, thanks for the notice.
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