Perfect,

close enough.

[EDIT]
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Thanks for your VERY reactive answer <3
Meanwhile, I found a trick that is even better in my case ; I set it up on 2 minutes every 15 minutes, and does not turn off the page (so if I stay with my work group and do not change conversation, I can still work.
Omg, I REALLY DO love your add-on !! Wish I could give more stars !!
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Does the job but a bit too perfectly as I set it up. I needed to stop Facebook. Well, it's done, and I'm glad with that.
But I need facebook/messages (Messenger) to keep working with some student groups ; is there a way to add some exceptions?
Thanks!
(I'd contribute if my bank account would allow me to.)

Much needed! Should be an inbuilt feature in the browsers :D. I love the "Block Set" feature, thereby I can categorize my distraction websites and set different block times for each set.

Probably a bug, but this extension slows firefox down to a crawl on Kubuntu 18.04 (up to date as of 02/25/19). Loading URL webpages takes significantly longer.

Very useful. Has all the features you would want from such an extension. Really improves productivity!
Developer is also very helpful and quick to respond to questions!

This thing is great if you have attention issues like me and love to switch to time wasting pages. Does what its supposed to do. Now if only I could make myself do that also.

This is a fantastic blocker, where I can specify precisely what I want! The only thing that I'd wish for is more than 6 block-sets, so that I can be even more specific about what I want to do with each site.

A functional and helpful addon to design time saving restrictions on the web and to eradicate bad online habits

Simple, feature-rich, and very transparent - great add-on!

I've been using leechblock for years. Great functionality, really improved my productivity. I recommend it to all my students.

Oh, performance... After deleting this add-on a CPU usage becomes 0-3% again (but it was 30%!)

Reliable and doesn't slow down my browser experience/performance in any way. I've used LeechBlock for years and it has kept me from succumbing to meaningless web browsing. Thank for for being free and doing a great job.

I really like the extension. It has all of the features that I require. My only issue is that twice now it deleted all of the blocks, settings, that I wrote for it, so I had to start with it from the beginning. Both times happened after I did some update..

Update: It seems this has been fixed. 5 stars for an awesome extension which helps keep me productive

[Edited] Nice plugin which works as expected AND has good support. Note: For the override feature to work, be sure to enable "[X] Allow temporary overrides" in options. This has stumped me, but the dev looked into it and figured out my problem, which means extra points for support. :-)

Great addon, but not recommended for laptop users, as it seems to eat CPU. Loading up the about:performance tab shows LeechBlock consistently consuming huge amounts of CPU whilst doing nothing. Had to reluctantly uninstall it.

Excellent !!!!

Great - very useful to keep addictive websites at bay