It loads the url before showing the "Restricted access" page, so it only visually blocks loading the page. I want something that never loads the page in the first place..

This is a particularly useful add-on if you are using the feature in Firefox 'DNS over HTTPS' (DoH), as DoH
bypasses your hosts file which is normally edited/used to block unwanted domains.

It is very easy to use

Perfect, this is exactly what I need to work. Liked the wildcard method for keyword.