NoDistractions - website blocker by AsciiJakob

Use if: You just want a simple add-on to block distracting websites when enabled, an extension that has an intuitive and straightforward UI.
Don't use if: You require very specific features such as blocking only being active at specific times of day. The add-on being active is merely meant to serve as a reminder that you have chosen to be productive.

Features:
- Sites are easy to add and doing so requires just two simple mouse clicks, you don't have to navigate through confusing menus.
- Blocking can easily be toggled on or off through a popup. A keybinding is also available (CTRL+ALT+D).
- The ability to temporarily visit a website (for just a minute or two) is available. It's possible to toggle this feature off in the settings, for those with bad impulse control.
- Being simple doesn't equate to not being powerful; advanced site patterns (using URL Match patterns) are available for users with more specific needs (see the help section of the popup).
- The extension is open-source, meaning that I am not afraid of hiding the code behind the extension and I allow users to contribute to it if they want to implement a feature.