/usr/lib/thunderbird/extensions/langpack-ru@lightning.debian.org is in lightning-l10n-ru 1:45.8.0-3~deb8u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/thunderbird/extensions/../../../share/iceowl/extensions/langpack-ru@lightning.debian.org