/usr/lib/ is in firefox-locale-nl 28.0+build2-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox/
/usr/lib/firefox/distribution/
/usr/lib/firefox/distribution/searchplugins/
/usr/lib/firefox/distribution/searchplugins/locale/
/usr/lib/firefox/distribution/searchplugins/locale/nl/
/usr/lib/firefox/distribution/searchplugins/locale/nl/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/nl/wikipedia-nl.xml
/usr/lib/firefox/distribution/searchplugins/locale/nl/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/nl/bolcom-nl.xml
/usr/lib/firefox/distribution/searchplugins/locale/nl/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/nl/marktplaats-nl.xml
/usr/lib/firefox-addons/
/usr/lib/firefox-addons/extensions/
/usr/lib/firefox-addons/extensions/langpack-nl@firefox.mozilla.org.xpi