I've never been unable to access a site on Firefox due to DRM. There is a prompt asking to run DRM-enabled media, but that's it.
Edit: or is there something about Manifest v3 that will get Firefox blocked somehow? IDK how as I would think it would be easy to pretend to be compliant.
They absolutely would've been able to grandfather users that paid before the subscription was added. Pure greed and they know you can't do anything about it aside from leaving a bad review.