Mindify

This add-on serves up a straightforward Yes/No question every 15 minutes: "Is this a productive use of your time?". Say "Yes", and you can continue using the domain at hand. Say "No", and every tab showing the unproductive domain shuts down and is prevented from reopening for the next 15 minutes. This 15min block is a unique chunk of time per domain.

In a way, this add-on is both a hard and soft blocker; it will block and close any domain in a straightforward manner, but at the same time it requires the honesty and resolve of the user to do so.

Unlike typical blockers that quietly work in the background, this one nudges you to actively engage with your web habits. The simple act of directly acknowledging the possible benefits or drawbacks of these habits can enhance awareness and eventual satisfaction in how you spend your time online, solidifying that resolve for future use. Beyond that, I just thought it was neat.

Note: The permission to "Access your data for all websites" is required simply because the add-on has to access any URL it is given in order to interact with the domain (and block it). This flags the required permission. This is subject to change in the future, for accessibility sake.