I should really find a good way to use the notification dismissal API I made (https://github.com/tootsuite/mastodon/pull/2251) on the frontend, but I'm not sure where you'd put the button..
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Like, the way notifications work atm is pretty inconsistent.
For replies, boosts and favourites, you've got the '...' drop down, but not for follows.
For follows, boosts and favourites you've got the 'so and so...' header, but not for replies.
You'd need one of these two to be consistent in order to place a 'dismiss' or an 'x' button or whatever.
