You can lie, but that doesnt mean that a website cant still tell your base OS if they use JS platform fingerprinting. Arkenfox, the base config which Librewolf is based off of says the exact same thing. Go to CreepJS and see it get your platform regardless.
Secondly, do you block all JS? NoScript is not a silver bullet and doesnt stop fingerprinting, it is itself identified by the CreepJS test site. It may in this case reduce the chance of OS fingerprinting, but pure CSS methods exist as well.
Additionally, NoScript is laregly redundant with uBlock Origin since you can do everything that it offers, such as blocking 3rd party scripts/iframes/all, block fonts, block JS, and it is very granular.
It's my understanding that websites can identify your OS and there's nothing we can realistically do about it, but it has something to do with how fonts are rendered. I'm not an expert, but this is what I recall from trying to obscure my OS from websites.
No script offers more than just is blocking you can block certain elements fonts what all that. It is NOT redundant. And creepjs doesn't even run without js which I don't allow on non trusted websites. Also yeah sorry I wasn't trying to be condescending.