$ git clone -n https://src.fedoraproject.org/rpms/firefox.git /var/lib/mock/f41-build-830835-14825/root/chroot_tmpdir/scmroot/firefox
Cloning into '/var/lib/mock/f41-build-830835-14825/root/chroot_tmpdir/scmroot/firefox'...
$ git fetch origin e909cb26bee439708833790bb092ea2c9dd9cef6:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/firefox
 * [new ref]         e909cb26bee439708833790bb092ea2c9dd9cef6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e909cb2 Eliminate use of obsolete %patchN syntax (#2283636)