/usr/include/thunderbird/mozilla/gfx/ is in thunderbird-dev 1:38.6.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/thunderbird/mozilla/gfx/2D.h
/usr/include/thunderbird/mozilla/gfx/BaseCoord.h
/usr/include/thunderbird/mozilla/gfx/BaseMargin.h
/usr/include/thunderbird/mozilla/gfx/BasePoint.h
/usr/include/thunderbird/mozilla/gfx/BasePoint3D.h
/usr/include/thunderbird/mozilla/gfx/BasePoint4D.h
/usr/include/thunderbird/mozilla/gfx/BaseRect.h
/usr/include/thunderbird/mozilla/gfx/BaseSize.h
/usr/include/thunderbird/mozilla/gfx/Blur.h
/usr/include/thunderbird/mozilla/gfx/BorrowedContext.h
/usr/include/thunderbird/mozilla/gfx/Coord.h
/usr/include/thunderbird/mozilla/gfx/DataSurfaceHelpers.h
/usr/include/thunderbird/mozilla/gfx/DrawTargetTiled.h
/usr/include/thunderbird/mozilla/gfx/Filters.h
/usr/include/thunderbird/mozilla/gfx/Helpers.h
/usr/include/thunderbird/mozilla/gfx/HelpersSkia.h
/usr/include/thunderbird/mozilla/gfx/Logging.h
/usr/include/thunderbird/mozilla/gfx/Matrix.h
/usr/include/thunderbird/mozilla/gfx/PathHelpers.h
/usr/include/thunderbird/mozilla/gfx/PatternHelpers.h
/usr/include/thunderbird/mozilla/gfx/Point.h
/usr/include/thunderbird/mozilla/gfx/Rect.h
/usr/include/thunderbird/mozilla/gfx/Scale.h
/usr/include/thunderbird/mozilla/gfx/ScaleFactor.h
/usr/include/thunderbird/mozilla/gfx/SharedDIB.h
/usr/include/thunderbird/mozilla/gfx/SourceSurfaceCairo.h
/usr/include/thunderbird/mozilla/gfx/Tools.h
/usr/include/thunderbird/mozilla/gfx/Types.h
/usr/include/thunderbird/mozilla/gfx/UserData.h