/usr/lib/ipxe/rtl8139.rom is in ipxe-qemu 1.0.0+git-20131111.c3d1e78-2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ipxe/qemu/pxe-rtl8139.rom
/usr/lib/ipxe/qemu/pxe-rtl8139.rom