/usr/include/thunderbird/harfbuzz/ is in thunderbird-dev 1:52.8.0-1~deb8u1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/thunderbird/harfbuzz/hb-blob.h
/usr/include/thunderbird/harfbuzz/hb-buffer.h
/usr/include/thunderbird/harfbuzz/hb-common.h
/usr/include/thunderbird/harfbuzz/hb-deprecated.h
/usr/include/thunderbird/harfbuzz/hb-face.h
/usr/include/thunderbird/harfbuzz/hb-font.h
/usr/include/thunderbird/harfbuzz/hb-glib.h
/usr/include/thunderbird/harfbuzz/hb-ot-font.h
/usr/include/thunderbird/harfbuzz/hb-ot-layout.h
/usr/include/thunderbird/harfbuzz/hb-ot-math.h
/usr/include/thunderbird/harfbuzz/hb-ot-shape.h
/usr/include/thunderbird/harfbuzz/hb-ot-tag.h
/usr/include/thunderbird/harfbuzz/hb-ot.h
/usr/include/thunderbird/harfbuzz/hb-set.h
/usr/include/thunderbird/harfbuzz/hb-shape-plan.h
/usr/include/thunderbird/harfbuzz/hb-shape.h
/usr/include/thunderbird/harfbuzz/hb-unicode.h
/usr/include/thunderbird/harfbuzz/hb-version.h
/usr/include/thunderbird/harfbuzz/hb.h