Comment # 29 on bug 1018741 from lists dev

> For the one-time boot, enter the "Boot Maintenance Manager" and choose "Boot
> From File" to find the specific efi image.

In the chroot'd guest, I set

  echo "fs0:\EFI\opensuse\grubx64.efi" > /boot/efi/startup.nsh

exit chroot
restart guest
enter OVMF config
select Boot Manager
select one-time EFI Shell

Shell appears, times out & falls through to startup.nsh

and fails at

Shell> fs0:\EFI\opensuse\grubx64.efi
Script Error Status: Security Violation (line number 1)
Shell>