Work Hard by Pedro FIlho

A simple, private and efficient way to block websites and keep you focused.

It gives you the power to block whatever you want, the main suggestion is to block entire domains, but you can block keywords, tags, categories, anything that can make you procrastinate.

The plugin itself just checks your tabs and close it if it matches anything you added on the list, simple and effective.

You should use it with some focus technique like the pomodoro one.

This extension doesn't store anything on any server, only on your computer. The code of this plugin is open source and you can check it out anytime you want.