Comment 66 for bug 774089

You may be able to install an old firmware version, if there was one for the 5,4.

I inadvertently installed an old firmware (1.3) on my 5,1 and it worked just fine.

I initally wrote Grub to the disk root, so I thought that might be the problem. But after updating the firmware I reinstalled Grub to the correct partition (0s3) and the same thing happened. Only the firmware updated itself automatically on first boot. Not sure if it was able to do that because I had just installed the firmware again or it was because I installed Grub correctly