/lib/udev/rules.d/50-firmware.rules is in udev 204-5ubuntu20.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | # do not edit this file, it will be overwritten on update
SUBSYSTEM=="firmware", ACTION=="add", RUN{builtin}="firmware"
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