Please tell me how you configured LeechBlock NG. I tried the delaying mode, but only works for the first visit of a domain? Once I've waited those seconds for the page to load I can mindlessly wander around for hours if I don't close the tab.
Link to the extension which in turn links to the git repo: https://addons.mozilla.org/en-US/firefox/addon/delaywebpage/
But the block repeats every few hours, and I'm pretty sure that clicking on a link within the same tab repeats the block then (maybe depends on the page). So yes, the "dosage" of how many delays you get is not very well controlled for. Still, I'm using this setup for years and it definitely does something for me.