Another difference is that Coreboot is essentially a rolling release, whereas Libreboot periodically takes a snapshot of upstream and maintains it for a while.

Another difference is that Coreboot is essentially a rolling release, whereas Libreboot periodically takes a snapshot of upstream and maintains it for a while. Libreboot is therefore something like a long-term service release. Anecdotally, I also found Libreboot easier to build. There is less configuration involved.