/usr/include/thunderbird/js/ is in thunderbird-dev 1:52.8.0-1~deb8u1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/thunderbird/js/CallArgs.h
/usr/include/thunderbird/js/CallNonGenericMethod.h
/usr/include/thunderbird/js/CharacterEncoding.h
/usr/include/thunderbird/js/Class.h
/usr/include/thunderbird/js/Conversions.h
/usr/include/thunderbird/js/Date.h
/usr/include/thunderbird/js/Debug.h
/usr/include/thunderbird/js/GCAPI.h
/usr/include/thunderbird/js/GCAnnotations.h
/usr/include/thunderbird/js/GCHashTable.h
/usr/include/thunderbird/js/GCPolicyAPI.h
/usr/include/thunderbird/js/GCVariant.h
/usr/include/thunderbird/js/GCVector.h
/usr/include/thunderbird/js/HashTable.h
/usr/include/thunderbird/js/HeapAPI.h
/usr/include/thunderbird/js/Id.h
/usr/include/thunderbird/js/Initialization.h
/usr/include/thunderbird/js/LegacyIntTypes.h
/usr/include/thunderbird/js/MemoryMetrics.h
/usr/include/thunderbird/js/Principals.h
/usr/include/thunderbird/js/ProfilingFrameIterator.h
/usr/include/thunderbird/js/ProfilingStack.h
/usr/include/thunderbird/js/Proxy.h
/usr/include/thunderbird/js/Realm.h
/usr/include/thunderbird/js/RequiredDefines.h
/usr/include/thunderbird/js/RootingAPI.h
/usr/include/thunderbird/js/SliceBudget.h
/usr/include/thunderbird/js/StructuredClone.h
/usr/include/thunderbird/js/SweepingAPI.h
/usr/include/thunderbird/js/TraceKind.h
/usr/include/thunderbird/js/TracingAPI.h
/usr/include/thunderbird/js/TrackedOptimizationInfo.h
/usr/include/thunderbird/js/TypeDecls.h
/usr/include/thunderbird/js/UbiNode.h
/usr/include/thunderbird/js/UbiNodeBreadthFirst.h
/usr/include/thunderbird/js/UbiNodeCensus.h
/usr/include/thunderbird/js/UbiNodeDominatorTree.h
/usr/include/thunderbird/js/UbiNodePostOrder.h
/usr/include/thunderbird/js/UbiNodeShortestPaths.h
/usr/include/thunderbird/js/UniquePtr.h
/usr/include/thunderbird/js/Utility.h
/usr/include/thunderbird/js/Value.h
/usr/include/thunderbird/js/Vector.h
/usr/include/thunderbird/js/WeakMapPtr.h