/usr/share/mozilla/extensions/{ec8030f7-c20a-464f-9b0e-13a3a9e97384}/{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/{ec8030f7-c20a-464f-9b0e-13a3a9e97384}/../../../xul-ext/tabmixplus