/usr/share/mozilla/extensions/{8de7fcbb-c55c-4fbe-bfc5-fc555c87dbc4}/{dc572301-7619-498c-a57d-39143191b318} is in xul-ext-tabmixplus 0.5.0.0-1~deb8u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/mozilla/extensions/{8de7fcbb-c55c-4fbe-bfc5-fc555c87dbc4}/../../../xul-ext/tabmixplus