/usr/include/thunderbird-11.0.1/md/ is in thunderbird-dev 11.0.1+build1-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/thunderbird-11.0.1/md/_aix32.cfg
/usr/include/thunderbird-11.0.1/md/_aix64.cfg
/usr/include/thunderbird-11.0.1/md/_beos.cfg
/usr/include/thunderbird-11.0.1/md/_bsdi.cfg
/usr/include/thunderbird-11.0.1/md/_darwin.cfg
/usr/include/thunderbird-11.0.1/md/_dgux.cfg
/usr/include/thunderbird-11.0.1/md/_freebsd.cfg
/usr/include/thunderbird-11.0.1/md/_hpux32.cfg
/usr/include/thunderbird-11.0.1/md/_hpux64.cfg
/usr/include/thunderbird-11.0.1/md/_irix32.cfg
/usr/include/thunderbird-11.0.1/md/_irix64.cfg
/usr/include/thunderbird-11.0.1/md/_linux.cfg
/usr/include/thunderbird-11.0.1/md/_ncr.cfg
/usr/include/thunderbird-11.0.1/md/_nec.cfg
/usr/include/thunderbird-11.0.1/md/_netbsd.cfg
/usr/include/thunderbird-11.0.1/md/_nextstep.cfg
/usr/include/thunderbird-11.0.1/md/_nto.cfg
/usr/include/thunderbird-11.0.1/md/_openbsd.cfg
/usr/include/thunderbird-11.0.1/md/_os2.cfg
/usr/include/thunderbird-11.0.1/md/_osf1.cfg
/usr/include/thunderbird-11.0.1/md/_qnx.cfg
/usr/include/thunderbird-11.0.1/md/_reliantunix.cfg
/usr/include/thunderbird-11.0.1/md/_riscos.cfg
/usr/include/thunderbird-11.0.1/md/_scoos.cfg
/usr/include/thunderbird-11.0.1/md/_solaris.cfg
/usr/include/thunderbird-11.0.1/md/_sony.cfg
/usr/include/thunderbird-11.0.1/md/_sunos4.cfg
/usr/include/thunderbird-11.0.1/md/_symbian.cfg
/usr/include/thunderbird-11.0.1/md/_unixware.cfg
/usr/include/thunderbird-11.0.1/md/_unixware7.cfg
/usr/include/thunderbird-11.0.1/md/_win95.cfg
/usr/include/thunderbird-11.0.1/md/_winnt.cfg