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