/usr/lib/firefox/ is in firefox-locale-vi 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-vi@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/vi/
/usr/lib/firefox/distribution/searchplugins/locale/vi/5giay.xml
/usr/lib/firefox/distribution/searchplugins/locale/vi/baambootratuav.xml
/usr/lib/firefox/distribution/searchplugins/locale/vi/creativecommons.xml
/usr/lib/firefox/distribution/searchplugins/locale/vi/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/vi/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/vi/muare.xml
/usr/lib/firefox/distribution/searchplugins/locale/vi/wikipedia-vi.xml
/usr/lib/firefox/distribution/searchplugins/locale/vi/zing-mp3.xml