/usr/lib/ is in firefox-locale-bg 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/bg/
/usr/lib/firefox/distribution/searchplugins/locale/bg/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/bg/diribg.xml
/usr/lib/firefox/distribution/searchplugins/locale/bg/pe-bg.xml
/usr/lib/firefox/distribution/searchplugins/locale/bg/portalbgdict.xml
/usr/lib/firefox/distribution/searchplugins/locale/bg/911bg.xml
/usr/lib/firefox/distribution/searchplugins/locale/bg/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/bg/wikipedia-bg.xml
/usr/lib/firefox/distribution/searchplugins/locale/bg/amazondotcom.xml
/usr/lib/firefox-addons/
/usr/lib/firefox-addons/extensions/
/usr/lib/firefox-addons/extensions/langpack-bg@firefox.mozilla.org.xpi