If you are a Facebook user - it was ironic: What a non-Facebook user today? - Then you will know the button exists, the link a table "I like" allowing the user uses it and will be understanding if you do not then the video, photo or the commentary you do not like just as well that things are black and white for Facebook.
However, the world consists of more things and sometimes we needed because of the remark about something that "we do not like" and for now at least we stayed with the desire to let him have the taste the rest of the world, space until a group of developers should create for the "Dislike Facebook"

Facebook Dislike is an addon that you can install in your favorite browser - Firefox is clear - and leave it in very clear that something does not please you, I am sure that after the half-time people to Facebook will echo the voices who ask this button.

addon, button, facebook, Firefox, don't Like this