I have been using raindrop.io for my bookmarks for seven years or so and it is pretty good. Comments all have permalinks as you know.
In Firefox, you can hover over the timestamp next to the name of the commenter, right-click (or whatever it is you Mac people do), and select Bookmark Link... to bookmark a comment.
Alternatively, you can click on the timestamp and then use whatever mechanism your OS/Browser allows to bookmark the page you go to as a result of the click.
Sometimes I see a comment I'd like to bookmark, but currently the only ways to save a comment are by subscribing to its replies (which sometimes produces unwanted notifications and requires me to check a different profile section than the rest of my bookmarks) or bookmarking the post it's attached to (which can be inconvenient for posts with many comments, and requires me to remember which comment the bookmark is actually for). Would it be possible to add a native bookmark option for comments?