$ git clone -n https://src.fedoraproject.org/forks/eclipseo/rpms/firefox.git /var/lib/mock/f43-build-60908998-6585414/root/chroot_tmpdir/scmroot/firefox
Cloning into '/var/lib/mock/f43-build-60908998-6585414/root/chroot_tmpdir/scmroot/firefox'...
$ git fetch origin 0b9ed0c6d10b66666fafe0b69091cd49ac5d63cf:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/forks/eclipseo/rpms/firefox
 * [new ref]         0b9ed0c6d10b66666fafe0b69091cd49ac5d63cf -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0b9ed0c Enable JXL by default and improve JXL support