This kind of tool, to make sense, needs to have as many people as possible on it otherwise you'll see no comment on any site you open. You can indeed leave a comment yourself, but probably people won't if they see nobody's ever going to read them.
So that's why it's strange that such an extension, which I think does have a social aspect, would ignore 60% of browsers.
If the data is open and federated (as it should be), it will still be available for ingestion by other future (and past) attempts at the idea. I don't see any fundamental problem with the idea, but understand that it's important to get the details right.
So that's why it's strange that such an extension, which I think does have a social aspect, would ignore 60% of browsers.