Here's a Chrome extension that is useful for enforcing the Pomodoro technique. It allows you to blacklist websites and customize the work/break lengths.
https://chrome.google.com/webstore/detail/strict-workflow/cg...
https://chrome.google.com/webstore/detail/strict-workflow/cg...
It forces you to make sure interruptions are actually worth dealing with vs putting them off till after the timer is up.