/usr/include/thunderbird/js/ is in thunderbird-dev 1:24.4.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/thunderbird/js/Anchor.h
/usr/include/thunderbird/js/CallArgs.h
/usr/include/thunderbird/js/CharacterEncoding.h
/usr/include/thunderbird/js/Date.h
/usr/include/thunderbird/js/GCAPI.h
/usr/include/thunderbird/js/HashTable.h
/usr/include/thunderbird/js/HeapAPI.h
/usr/include/thunderbird/js/LegacyIntTypes.h
/usr/include/thunderbird/js/MemoryMetrics.h
/usr/include/thunderbird/js/PropertyKey.h
/usr/include/thunderbird/js/RequiredDefines.h
/usr/include/thunderbird/js/RootingAPI.h
/usr/include/thunderbird/js/TemplateLib.h
/usr/include/thunderbird/js/Utility.h
/usr/include/thunderbird/js/Value.h
/usr/include/thunderbird/js/Vector.h