This is the best site blocking add-on.

The new(er) version does not work well, after I load all my blocking page via a textfile, everything is working. But after a restart, I can see the blocked site, but when I click on a link from a blocked site (going to a sub link) it start blocking. When I save for example a new website to block, everything is working good again. But after a restart same problems. In the past I used it with succes, but now there is something not quite right.

So far so good in the first 5 or so minutes. I needed it to stop me from accidentally watching any video sites while having a VPN with limited gb per month available.

Fantastic! Does exactly what it says and there's lots more under the hood. A pity it's not compatible with Firefox Mobile.

Excellent. Fantastic options. Just what I was looking for (for my autistic son).

This extension is a no-frills, functional block site extension. I personally like using their timed close feature, which closes websites that you blocked automatically so there aren't any distractions. Highly recommend.