A couple of years ago I was pretty addicted to Facebook and would compulsively open a new tab and start typing "f..." in the address bar. Even if I had another tab with Facebook open.

I tried blocking it for lapses of time but it didn't reduce my addiction. What did work was logging out of Facebook. The annoyance of having to log in and stop my flow was enough for me to stop using Facebook. Now I use it less than once a month when I want to contact some company that only has a Facebook page.