[byte1918]

You can configure Leechblock (1) to do this. You have to configure it to show the 'Delaying page'.

(1) - https://addons.mozilla.org/en-US/firefox/addon/leechblock-ng...

[unicornporn]

I tried that, 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.

[byte1918]

there's a checkbox `Block only first accessed page of site when delaying page is used`. Uncheck it.