/usr/ is in firefox-locale-ru 28.0+build2-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/
/usr/lib/firefox/
/usr/lib/firefox/distribution/
/usr/lib/firefox/distribution/searchplugins/
/usr/lib/firefox/distribution/searchplugins/locale/
/usr/lib/firefox/distribution/searchplugins/locale/ru/
/usr/lib/firefox/distribution/searchplugins/locale/ru/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/ru/wikipedia-ru.xml
/usr/lib/firefox/distribution/searchplugins/locale/ru/yandex-slovari.xml
/usr/lib/firefox/distribution/searchplugins/locale/ru/yandex.xml
/usr/lib/firefox/distribution/searchplugins/locale/ru/priceru.xml
/usr/lib/firefox/distribution/searchplugins/locale/ru/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/ru/mailru.xml
/usr/lib/firefox/distribution/searchplugins/locale/ru/ozonru.xml
/usr/lib/firefox-addons/
/usr/lib/firefox-addons/extensions/
/usr/lib/firefox-addons/extensions/langpack-ru@firefox.mozilla.org.xpi
/usr/share/
/usr/share/doc/
/usr/share/doc/firefox-locale-ru/
/usr/share/doc/firefox-locale-ru/copyright
/usr/share/doc/firefox-locale-ru/changelog.Debian.gz