These Terms only apply to the Executable Code version of Firefox, not the Firefox source code.

www.mozilla.org/en-US/about/legal/terms/firefox/

Thus, the answer turns in whether any Firefox binaries are used or distributed with LibreWolf. On their website, I don’t even see any binaries for LibreWolf that they host, except the Windows binary. For all other OS, they refer to that OS’s package manager. But we’ve still, there is nothing to suggest that any Mozilla-compiled binaries are in LibreWolf.

The answer appears to be: no.