/usr/src/linux-headers-3.19.0-71-lowlatency/firmware is in linux-headers-3.19.0-71-lowlatency 3.19.0-71.79~14.04.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-3.19.0-71-lowlatency/../linux-headers-3.19.0-71/firmware