Facebook allows you to share links, videos, pictures etc with your friends. Sometimes people like the shared content and they can express this by hitting the Like button, but there is no option for disliking the shared content till now, so they can’t show their disapproval on any shared content.
However if you are a firefox user, then with the help of facebook dislike add-on, you can get a dislike button to show your dissatisfaction on any shared link, pictures, videos etc. So install the facebook dislike add-on from this link: Facebook dislike add-on.
Once this add-on is installed you will find a dislike button on every shared content at faceboook. In the screenshot above you can easily notice the Dislike button in between Unlike and Share button.
For more facebook how to guides head over to this page: http://virgintech.org/tag/facebook