$ git clone -n https://src.fedoraproject.org/rpms/firefox.git /var/lib/mock/f41-build-1208203-22498/root/chroot_tmpdir/scmroot/firefox
Cloning into '/var/lib/mock/f41-build-1208203-22498/root/chroot_tmpdir/scmroot/firefox'...
$ git fetch origin fec72bef9f44cb4ccec4aed514edafaec8d125d8:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/firefox
 * [new ref]         fec72bef9f44cb4ccec4aed514edafaec8d125d8 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at fec72be Update to 127.0.2