I suggest hash of some normalized version of the URL or you run into privacy issues. People won't use the extension if it tells relays all the pages they are visiting. Even with hashing, people will quickly learn the hash of pornhub but at least you won't leak any credentials that are encoded in the url. 

 Smart 👆

Maybe we need a NIP to define what to hash.  

 I bet chatgpt is helpful here. The idea of this chat plugin is not new. rbutr and dissenter did it before. It never caught on I guess. With nostr, the comments will leak into social clients and if done right, help both in a feedback loop.