I wrote a css override to make it more encouraging.
The code below makes the custom message you write look fancier, and removes the discouraging ! sign. I'd much rather block sites gently.
Thank you for such an awesome plugin though.

body {
background-image: url(https://source.unsplash.com/collection/139386/1920x1080/?sig=) !important;
background-repeat: no-repeat;
background-size: cover;

}
h1, table, #exception,#options, #switch,footer,header{
display:none !important;
}
#message {
width: 100%;
text-align: center;
font-size: 5em;
padding: 0 !important;
height: 100%;
display: flex;
align-items: center;
justify-content: center;
font-weight: 100;
background: #222222ba;
margin: 0 !important;
}

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).