/usr/lib/x86_64-linux-gnu/libnautilus-extension.so.1 is in libnautilus-extension1a 1:3.18.4.is.3.14.3-0ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libnautilus-extension.so.1.4.0