$ git clone -n https://src.fedoraproject.org/rpms/firefox.git /var/lib/mock/f38-build-side-42-init-devel-1038945-29748/root/chroot_tmpdir/scmroot/firefox
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-1038945-29748/root/chroot_tmpdir/scmroot/firefox'...
$ git fetch origin 60bfa9889d4fea112cfddb6854087f8095d4999c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/firefox
 * [new ref]         60bfa9889d4fea112cfddb6854087f8095d4999c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 60bfa98 Added Canvas/WebGL VA-API playback patch (D167159 / mzbz#1769747)