/usr/include/thunderbird/mozilla/ipc/ is in thunderbird-dev 1:52.8.0-1~deb8u1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/thunderbird/mozilla/ipc/BackgroundChild.h
/usr/include/thunderbird/mozilla/ipc/BackgroundParent.h
/usr/include/thunderbird/mozilla/ipc/BackgroundUtils.h
/usr/include/thunderbird/mozilla/ipc/BrowserProcessSubThread.h
/usr/include/thunderbird/mozilla/ipc/CrashReporterClient.h
/usr/include/thunderbird/mozilla/ipc/CrashReporterHost.h
/usr/include/thunderbird/mozilla/ipc/CrashReporterMetadataShmem.h
/usr/include/thunderbird/mozilla/ipc/CrossProcessMutex.h
/usr/include/thunderbird/mozilla/ipc/DBusConnectionDelete.h
/usr/include/thunderbird/mozilla/ipc/DBusConnectionRefPtr.h
/usr/include/thunderbird/mozilla/ipc/DBusHelpers.h
/usr/include/thunderbird/mozilla/ipc/DBusMessageRefPtr.h
/usr/include/thunderbird/mozilla/ipc/DBusPendingCallRefPtr.h
/usr/include/thunderbird/mozilla/ipc/DBusUtils.h
/usr/include/thunderbird/mozilla/ipc/DBusWatcher.h
/usr/include/thunderbird/mozilla/ipc/FileDescriptor.h
/usr/include/thunderbird/mozilla/ipc/FileDescriptorSetChild.h
/usr/include/thunderbird/mozilla/ipc/FileDescriptorSetParent.h
/usr/include/thunderbird/mozilla/ipc/FileDescriptorUtils.h
/usr/include/thunderbird/mozilla/ipc/GeckoChildProcessHost.h
/usr/include/thunderbird/mozilla/ipc/IOThreadChild.h
/usr/include/thunderbird/mozilla/ipc/IPCStreamUtils.h
/usr/include/thunderbird/mozilla/ipc/InputStreamUtils.h
/usr/include/thunderbird/mozilla/ipc/MessageChannel.h
/usr/include/thunderbird/mozilla/ipc/MessageLink.h
/usr/include/thunderbird/mozilla/ipc/Neutering.h
/usr/include/thunderbird/mozilla/ipc/ProcessChild.h
/usr/include/thunderbird/mozilla/ipc/ProtocolUtils.h
/usr/include/thunderbird/mozilla/ipc/RawDBusConnection.h
/usr/include/thunderbird/mozilla/ipc/ScopedXREEmbed.h
/usr/include/thunderbird/mozilla/ipc/SendStream.h
/usr/include/thunderbird/mozilla/ipc/SendStreamAlloc.h
/usr/include/thunderbird/mozilla/ipc/SharedMemory.h
/usr/include/thunderbird/mozilla/ipc/SharedMemoryBasic.h
/usr/include/thunderbird/mozilla/ipc/SharedMemoryBasic_chromium.h
/usr/include/thunderbird/mozilla/ipc/Shmem.h
/usr/include/thunderbird/mozilla/ipc/TaskFactory.h
/usr/include/thunderbird/mozilla/ipc/TestShellChild.h
/usr/include/thunderbird/mozilla/ipc/TestShellParent.h
/usr/include/thunderbird/mozilla/ipc/Transport.h
/usr/include/thunderbird/mozilla/ipc/Transport_posix.h
/usr/include/thunderbird/mozilla/ipc/URIUtils.h
/usr/include/thunderbird/mozilla/ipc/WindowsMessageLoop.h
/usr/include/thunderbird/mozilla/ipc/XPCShellEnvironment.h