I asked this elsewhere but didn't get a good answer.

One thing I've been looking for is a social media platform that allows you to comment about any page on the Internet. For example, such a platform would be very useful when you want to discuss a YouTube video that has commenting disabled. Gab's Dissenter best fits the bill: it works by mapping a forum thread to each website visited by its users. Anyone with the Gab extension installed would be able to see the comments. However, the problem is that Gab is known for its alt-right user base. I obviously don't want anything to do with them. So are there any viable alternatives?

The "comment anywhere" extensions I did find on the Chrome store are for comments that only the user can see, much akin to Post-it Notes.