/usr/lib/thunderbird-devel-11.0.1/idl is in thunderbird-dev 11.0.1+build1-0ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/thunderbird-devel-11.0.1/../../share/idl/thunderbird-11.0.1
/usr/lib/thunderbird-devel-11.0.1/../../share/idl/thunderbird-11.0.1