/usr/lib/firefox/webapprt/extensions/langpack-ko@firefox.mozilla.org.xpi is in firefox-locale-ko 45.0.2+build1-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/firefox/webapprt/extensions/../../../firefox-addons/extensions/langpack-ko@firefox.mozilla.org.xpi