Once I became aware of the "slot machine" effect of websites I deleted the default autocompletes for Facebook and Hacker News, for example.
Prior to doing this, if I typed "F" into chrome I went to my Facebook news feed, and "N" in chrome took me to HN.
I deleted those defaults and made it so the autocomplete takes it to my profile on each site. My Facebook profile page is inherently non addictive. It's just me. I can then choose to click on events or whatever.
My HN profile is even more boring. This forces me to make one extra click before viewing the news stories but that single click is enough to stop me from compulsively checking news.
I can't overstate how many hours per week I reclaimed from this one change. It is better for my purposes than any sort of focus blocker. It doesn't prevent me from doing anything, it just removes the addictive trigger.
I also moved my Facebook app from the first screen on my iPhone, and disallowed any notifications. This is better for me than deleting the app. As long as I don't see the little red circle with a number, there's no compulsive reminder.
As a consequence of using this technique I am able to get what I want from web services without the addictive component.
--edit: grammar--