You can use something like StayFocusd to force yourself off it. It won't allow you to reach the distracting websites no matter what you do. Forced boredom.

Though personally I've found if I just log out of facebook and my personal email, that helps. I can't open a tab and have rewards in less than 2 seconds. The extra few seconds to type in a password slows me down enough to just close the tab again and get back to work.