The addon is a webextension version of the Leechblock addon and helps me not wasting time (apart from writing a review when I should be studying ;-)).
You can block a list of domains or load a list of domains from an url. You can configure the day(s) of the week and the hours and minutes (eg. 0700-1700).
You can block yourself from undoing these settings and even disable the addon page of Firefox (be careful, you could lock it forever) to hinder yourself from disabling the addon.

Great on my PC but not on my phone. Each time I reopen Firefox on my phone it seems to reset the counter.

A wonderful add-on that allows you to increase your productivity by limiting your website access.

Great addon, good for blocking facebook when your getting drunk , and easy to use. Give this guy a clap or even better, a donation

Really love this add-ons, thanks LeechBlock!

I have trouble going to bed on time because I lose my sense of time when I read. Setting up a leachblock set to block everything after 10:30pm gives me the Shelling fence to go to bed.

I can limit waisted time on news and social media, and also limit my work from home

FINALLY! I was looking for a good Blocking App to restrict myself from wasting time. The only other I found - "Block Site" - is a piece of garbage that doesn't work at all how you expect it to work. This one does! Congratz!

Exactly what I was looking for, and with all the options I need

Great for homeschoolers. Keeps kids off their favorite websites until school is over.

Great add-on, lots of options and easy to set up. LOVE IT!

At the moment of writing this review (29-01-2018) it's the only reliable option available to block sites in Firefox Quantum.

Great Addon! Easy to handle and helped me lose the habit of checking pointless news every few minutes when working on challenging tasks.

This is the ONLY extension you need if you want to kick bad internet habits, quit porn, or just reclaim the time spent online. Can not thank the developers enough. Thanks Leechblock!

I honestly recommend this addon to everybody I know. I have a pretty bad internet addiction, and leechblock has helped so much. I finally feel like I'm in control of my social media use, instead of letting it control my life!

This add-on helps me waste way less time on the web.
It has a good number of features to specify on which day and at what time to block sites.
Very useful of anyone suffering from procrastination. :D

Great addon to prevent compulsively wasting time

I was so glad to find out this extension existed. I used it to block Facebook, which has significantly improved my quality of life. It's highly customisable too, so no complaints.

I love this extension, it helps keep me focused and more in control of my digital life.