It doesn't really matter whether it was "targeted" at Firefox specifically or not, what matters is whether the website has logic that discriminates against Firefox users. Those are 2 different things. "End" vs "means".

I wouldn't be surprised if the logic was written by some AI, without specifically targeting any browser, and from the training data the AI concluded that there's a high enough chance of adblocking to deserve handicapping the UX when the browser happens to be Firefox's. Given that all it's doing is slowing the website down (instead of straight out blocking them) it might be that this is just a lower level of protection they added for cases where there's some indicators even if there's not a 100% confidence an adblock is used.