/usr/lib/thunderbird-addons/ is in xul-ext-gdata-provider 1:52.7.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/thunderbird-addons/extensions/
/usr/lib/thunderbird-addons/extensions/{a62ef8ec-5fdc-40c2-873c-223b8a6925cc}/
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