/usr/lib/firefox/ is in firefox-locale-nb 11.0+build1-0ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox-addons/extensions/
/usr/lib/firefox-addons/extensions/langpack-nb-NO@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/nb-NO/
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/amazon-en-GB.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/bok-NO.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/qxl-NO.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/telefonkatalogen-NO.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/wikipedia-NO.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/yahoo-NO.xml