/usr/lib/thunderbird/extensions/langpack-pt-br@lightning.debian.org is in lightning-l10n-pt-br 1:52.8.0-1~deb8u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/thunderbird/extensions/../../../share/lightning/extensions/langpack-pt-br@lightning.debian.org