Since LibreWolf is libre software, it’s likely that a user has freedom to tweak this maybe via about:config. You just need to ask this directly in the LibreWolf community.
I think I know what you’re talking about, though. Perhaps CSS @font is forbidden, because many sites use Google fonts, which allows them to track you.
If Tor Browser is acceptable, give it a try. While TB too has very strict font restrictions to avoid finger-printing (so that a remote site may not know which fonts your system already has), web fonts are allowed by default. It’s relatively harder to distinguish/track individual Tor users, since TB hides your real IP & by default cookies are per session only.
LibreWolf shows your real IP, so it’s understandable and reasonable that it wants to be more careful about fonts. Still a user should be given freedom to do whatever, at their own risk. That’s what free software is all about, after all. Just a thought…