Adversarial compatibility is a good thing for users.
If the site doesn't want to implement what your extension would do then either they will try to shake you down, buy you out, or implement the feature on their site. The latter two seem like a positive for you.
I think people are going to use it(a few millions people could need it and there is no solutions available today), but I don't think it would be important enough for them to ever pay.
I don't think browser extensions are good to monetize.
Personally I would never pay to any of it.
I donated to two open source projects that are browser extensions but I don't think that's the target of you.
If you can't control the site I wouldn't pay for an extension that could easily break.
The artifact is being released for free. But you want to be compensated for your dev time. So maybe a patreon or github sponsorship or something like that.
What about a freemium model? Allow users to get basic features for free, but add hooks into the UI prompting them to upgrade to access more advanced features.
