If we want to like any post or any activity of facebook we can, but if we want to hate this posts or others activity we can't it. Officially facebook does not declared any dislike button, but we use dislike button from now. Just follow this simple steps. (you can use it only Firefox browser)
At first click this link and install in your firefox (only 15kb) Add Link
And then restart you browser. That's OK now enjoy dislike button like above picture.