/usr/src/linux-headers-4.4.0-91/drivers/firmware/ is in linux-headers-4.4.0-91 4.4.0-91.114.
This file is owned by root:root, with mode 0o755.
..
/usr/src/linux-headers-4.4.0-91/drivers/firmware/Kconfig
/usr/src/linux-headers-4.4.0-91/drivers/firmware/Makefile
/usr/src/linux-headers-4.4.0-91/drivers/firmware/broadcom/
/usr/src/linux-headers-4.4.0-91/drivers/firmware/broadcom/Kconfig
/usr/src/linux-headers-4.4.0-91/drivers/firmware/broadcom/Makefile
/usr/src/linux-headers-4.4.0-91/drivers/firmware/efi/
/usr/src/linux-headers-4.4.0-91/drivers/firmware/efi/Kconfig
/usr/src/linux-headers-4.4.0-91/drivers/firmware/efi/Makefile
/usr/src/linux-headers-4.4.0-91/drivers/firmware/efi/libstub/
/usr/src/linux-headers-4.4.0-91/drivers/firmware/efi/libstub/Makefile
/usr/src/linux-headers-4.4.0-91/drivers/firmware/efi/test/
/usr/src/linux-headers-4.4.0-91/drivers/firmware/efi/test/Makefile
/usr/src/linux-headers-4.4.0-91/drivers/firmware/google/
/usr/src/linux-headers-4.4.0-91/drivers/firmware/google/Kconfig
/usr/src/linux-headers-4.4.0-91/drivers/firmware/google/Makefile