$ git clone -n https://src.fedoraproject.org/rpms/firefox.git /var/lib/mock/f40-build-798494-141958/root/chroot_tmpdir/scmroot/firefox
Cloning into '/var/lib/mock/f40-build-798494-141958/root/chroot_tmpdir/scmroot/firefox'...
$ git fetch origin 364db1a5532f1fbd16716113d97b3a6ed0896c55:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/firefox
 * [new ref]         364db1a5532f1fbd16716113d97b3a6ed0896c55 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 364db1a everted IM patch