/usr/share/mozilla/extensions/{718e30fb-e89b-41dd-9da7-e25a45638b28}/calendar-timezones@mozilla.org is in xul-ext-calendar-timezones 1.3+build1-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/mozilla/extensions/{718e30fb-e89b-41dd-9da7-e25a45638b28}/../../../xul-ext/calendar-timezones