I'm not sure if this has already been suggested, but if it hasn't been, then maybe you could market/describe your add-on as one that prevents sneaky websites from tracking you.

And instead of calling it a anti-paywall add-on, instead call it a anti-tracking add-on.

If you do that though, you may be asked to explain the list of websites for which the add-on activates. I guess you'll need to have some sort of "valid" explanation for that.