I use SelfControl for website blocking on Mac. It works perfectly for me, and it is free. SelfControl blocks websites for a certain amount of time across all browsers. Even if the computer is shutdown and restarted, the app still blocks the websites. Also, there is a whitelist feature if you would only like to be able to visit certain websites.
Went to "GET IT" then saw the testimonial signed "GFW User", got really confused since GFW auto-trans into "Great FireWall" for me, then realized they have the same acronym. And they happen to have similar functionality. XD
OMG.... absolutely the BEST ...... I litterally giggle now everytime I pull up twitter or insta .... so g'damn funny! Yo... can you add developers.facebook.com to your "safe" site?
Creately