- Upgrade your firmware from High Sierra installed in an APFS drive:
A lot of people report that can't upgrade the BootROM from High Sierra installed with HFS+, so use a new/empty drive to install High Sierra from an APFS partition. Btw, Mojave requires APFS.
Thanks for posting this thread with this information you've compiled. You've provided much more useful information than Apple's vague 2 line knowledge base.
Found this thread and read about the High Sierra disk must be APFS after half the day wasted on failed attempts not having any idea what was going on.
This point above is particularly important and Apple absolutely does not mention this anywhere and their installer fails to provide this info to the user. Due to laziness or incompetence or just not giving a sheeeeeeet, Apple's installer tells user click Restart Button to start the firmware upgrade. The installer will do nothing and all for 15 -20 mins and restart itself get back to the same window.
In my case, I had Mojave on a bootable USB HFS, before even getting to the firmware it tells me my Video card isn't supported, well, Apple, dude, it must work, It's probably just gona suck, but I can handle just for installation because I need a boot screen.
So ok pull out all the other SSD, reset PRAM, connect the monitor to the Radeon RX 580 without bootscreen...fire it up...nothing black screen forever...Why, no one knows..pull out the Nvidia GT120, reboot, yah finally get to the installer, but What-TF, the Firmware upgrade does not respond, machine does nothing. Apple hates their users!!!
The Installer fails to check requirements and alert user exactly what is required for successful firmware upgrade. Had it said USB must be APFS and or a working High Sierra installed on a APFS disk is required for this firmware upgrade it would have saved me many hours.
So I decided to run the Mojave installer a High Sierra partition.
I still have Snow Leopard on the Mac Pro so my High Sierra partition was HFS to access the data from Snow Leopard. Firmware failed with this strategy too. Still no idea why until I read this thread bout USB can't be used to upgrade the firmware and the High Sierra working partition must be APFS. WhyTF Apple not mention this anywhere.
So with this info I set about to find another SSD to be used for High Sierra install. I created USB boot disk from a saved High Sierra installer.app from 2 years ago or whatever, booted machine get to start installation, it tells me installer is damaged, WTF, damaged, how?? eh
I used it before years ago it wasn't damaged. Turns out, this is misleading, it's actually a certificate expired. OMG, why on earth they need a certificate on macOS, this isn't an iPhone. Second, WhyTF, when running the 'create installer media' command doesn't a script run to check the certificate in the first place, If cert is expired download a new one and put in USB installer instead of wasting my time booting then getting this message. Alternatively and less convenient, at the very least, tell me I need to download a new version of the Installer. No, I don't prefer wasting data on downloads and my time at 1MB/sec on those damned slow servers.
If that is too hard, instead of the misleading message why not be transparent and tell us it is the certificate, and what to do about it, why all the cloak and dagger BS...I had an Ethernet cable hooked up, installer could have checked for expired cert, then checked the network find a new one and authenticate then run the installer without me even knowing and "just work" instead of pushing all the issues back to the user....What has happed at Apple, Apple forgot about "it just works"?
So then, I waste more time re-download a new High Sierra installer App, damn their servers can be slow.
I created the USB bootable High Sierra installer, format the SSD to APFS, installed successfully High Sierra.
So finally, launched the Mojave installer from the High Sierra APFS SSD, rebooted and yay, clicked restart button to upgrade the firmware, after 5 seconds machine shutdown, got the new firmware then finally got the Mojave installer process running.
Man, an entire day spent screwing around with this, should have taken 2 hours max.
Mac Pro now has the updated firmware but still refuses to start up with the Nvidia GT120 card in a PCI slot, even with not display connected to it. Other guys boot ok with the card in a slot and even Mojave will run with a display connected to the card, albeit slow, but who cares it's purpose now is purely needed for boot screen. That's another topic for research, not help from Apple.