/usr/include/thunderbird/vpx/ is in thunderbird-dev 1:38.6.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/thunderbird/vpx/arm.h
/usr/include/thunderbird/vpx/mem.h
/usr/include/thunderbird/vpx/vp8.h
/usr/include/thunderbird/vpx/vp8cx.h
/usr/include/thunderbird/vpx/vp8dx.h
/usr/include/thunderbird/vpx/vpx_codec.h
/usr/include/thunderbird/vpx/vpx_decoder.h
/usr/include/thunderbird/vpx/vpx_encoder.h
/usr/include/thunderbird/vpx/vpx_frame_buffer.h
/usr/include/thunderbird/vpx/vpx_image.h
/usr/include/thunderbird/vpx/vpx_integer.h
/usr/include/thunderbird/vpx/vpx_mem.h
/usr/include/thunderbird/vpx/vpx_mem_intrnl.h
/usr/include/thunderbird/vpx/vpx_scale.h
/usr/include/thunderbird/vpx/vpx_timer.h
/usr/include/thunderbird/vpx/x86.h
/usr/include/thunderbird/vpx/yv12config.h