I'm quite sure that Qemu 1.6.1 and 1.7.0rc cannot run vmdk v3 images. What qemu version did you use?
$ qemu-img info junos-vsrx-12.1X44-D10.4-domestic-disk1.vmdk qemu-img: 'image' uses a vmdk feature which is not supported by this qemu version: VMDK version 3
qemu-img: Could not open 'junos-vsrx-12.1X44-D10.4-domestic-disk1.vmdk': Could not open 'junos-vsrx-12.1X44-D10.4-domestic-disk1.vmdk': Wrong medium type
If it helps, I used VMWare Player 5.0.2 build-1031769 to import the Firefly VMDK and do whatever magic happens when you import the vmdk to vmware player.
I do not know why you must import with vmware player and use the newly created vmdk from the import. you cannot just use the vsrx vmdk. I havent figured out why but I am trying to. vmware player does something to the vmdk that makes qemu happy.