In a statement, Facebook said: "We are not testing a dislike button". So, as users get to downvote certain comments, it would give Facebook a clearer picture of what users want to see and the topics they are interested in.
Facebook has long faced an issue over how best to let people express less-than-positive feelings about people's posts and comments. The already existing "hide" button is not readily accessible right now, and does not bring the comment to Facebook's notice for being inappropriate.
In 2015, Facebook Design Chief Julie Zhuo said she had heard users complain about only having the ability to "like" a comment.
Facebook started testing a new feature that's "downvote" on comments of users, in order to make feedback easier. And as many know, Facebook doesn't mind copying the traits and features of competitors that it sees as successful.
In case you are wondering if its a "dislike button", its not, at least that is what Facebook is saying. Downvoting was popularized on Reddit for crowdsourcedcomment ranking.
The test was reported earlier by the Daily Beast. The option has begun to deal with the negative comments of any public post.
Facebook, however, has been very keen to stress that this isn't going to be a "dislike" feature. It's not a way of disliking posts, sadly, but is instead used to flag them.