/usr/include/firefox/mozilla/ipc/ is in firefox-dev 11.0+build1-0ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/firefox/mozilla/ipc/AsyncChannel.h
/usr/include/firefox/mozilla/ipc/BrowserProcessSubThread.h
/usr/include/firefox/mozilla/ipc/DocumentRendererChild.h
/usr/include/firefox/mozilla/ipc/DocumentRendererNativeIDChild.h
/usr/include/firefox/mozilla/ipc/DocumentRendererNativeIDParent.h
/usr/include/firefox/mozilla/ipc/DocumentRendererParent.h
/usr/include/firefox/mozilla/ipc/DocumentRendererShmemChild.h
/usr/include/firefox/mozilla/ipc/DocumentRendererShmemParent.h
/usr/include/firefox/mozilla/ipc/GeckoChildProcessHost.h
/usr/include/firefox/mozilla/ipc/IOThreadChild.h
/usr/include/firefox/mozilla/ipc/ProcessChild.h
/usr/include/firefox/mozilla/ipc/ProtocolUtils.h
/usr/include/firefox/mozilla/ipc/RPCChannel.h
/usr/include/firefox/mozilla/ipc/ScopedXREEmbed.h
/usr/include/firefox/mozilla/ipc/SharedMemory.h
/usr/include/firefox/mozilla/ipc/SharedMemoryBasic.h
/usr/include/firefox/mozilla/ipc/SharedMemoryBasic_chromium.h
/usr/include/firefox/mozilla/ipc/SharedMemorySysV.h
/usr/include/firefox/mozilla/ipc/Shmem.h
/usr/include/firefox/mozilla/ipc/SyncChannel.h
/usr/include/firefox/mozilla/ipc/TestShellChild.h
/usr/include/firefox/mozilla/ipc/TestShellParent.h
/usr/include/firefox/mozilla/ipc/Transport.h
/usr/include/firefox/mozilla/ipc/Transport_posix.h
/usr/include/firefox/mozilla/ipc/XPCShellEnvironment.h