/usr/share/mozilla/extensions/{3550f703-e582-4d05-9a08-453d09bdfdc6}/foxyproxy@eric.h.jung is in xul-ext-foxyproxy-standard 3.4-1.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/mozilla/extensions/{3550f703-e582-4d05-9a08-453d09bdfdc6}/../../../xul-ext/foxyproxy-standard