Qubes OS VS Libreboot

QubesOS and Trisquel are both operating systems. That means they run AFTER the machine has already been initalized (booted) using the BIOS. Libreboot is a replacement for the BIOS that come in most machines, which is proprietary.
Advantages of Libreboot over other BIOS? Faster boot, especially because it has GRUB built-in. Secure by default, there are no back doors written in, being free software you can inspect the code or have someone doing it for you. Also, Libreboot makes a better use of the Thinkpad machine than the default BIOS, for example it gives more memory to the graphics card (256 vs 32 mbs).
On top of Libreboot you need an OS which you can choose. I don't know if QubesOS is supported or not. Check the website.
HOWEVER, I know Qubes is supposed to be a high level of security, and I can accept that since you have multiple Virtual Machines running and all of that... however my understanding is that there is still proprietary software running in your system and therefore you must accept that there might be a backdoor. Trisquel is 100% free software and therefore better in that regard. If you are willing to take the time, you can make Trisquel as secure as other distros. It is a matter of not being so by default.

Unfortunately Qubes OS is only supported by Coreboot.
I love the approach of Qubes OS by compartmentalize every aspect of your digital life in cubes(VMs).
This makes me not accept the idea of having a single point of failure (in this case Trisquel) because i believe that we can benefit from Xen which has low attack of surface since has less lines of code compared to other Type 1 Hypervisors.Plus the fact that i think we need to compartmentalize our browsing habits.

A nice thing would be to have an X200 with Libreboot as a BIOS and Qubes OS based on Trisquel/Parabola Templates instead of Fedora/Debian.

Like I said, I am not familiar with QubesOS support, however if it is only supported by Coreboot, it might mean that there are non-free dependencies. I might be wrong.
Anyway, the difference you asked was about Qubes and Libreboot, I hope I clarified your question.

Depends on your threat model I guess, I prefer to go with Libreboot and Trisquel, even though if I was in a higher threat level I would maybe do something different.