I don't know how to write regular expressions and had no interest in learning at this point. It works just as well (unlike Block Site, for me). You just type the URL. Done.

Simple to use, works exactly as advertised, very effective, no clutter.

Good idea, but No hide option or password protection.

Excellent! Does exactly what is says.
Perfect for sophisticated URL blocking.

Exactly what I am looking for!

As simple as possible. Well, as long as you know regular expressions.

Good

good at preventing dns redirection to isp searchengine due to url not found

URL blocking by using regular expressions - the best way! Best blocking plugin for Firefox Quantum

Instead of having you advance and then deadend on a blank page, could you have it throw a little pop-up/toast saying that the page is blocked on the page without taking you away from the page you were on originally?

Ancestry, for instance, doesn't tell you which sources you can access for free and which ones they will harass you to pay for. This feature allows you to click the links and keep going down the line if you block the "give us money" page it redirects to if that resource is not available for free. Not having to backtrack and click again every time makes research go *much* faster.

Wow this is exactly what I was finding for...

Best website blocker that I could find. Great job allowing for regex and super simple and easy to use. Love it! :)

It's currently got a strict_max_version set to Firefox 56 in the manifest. Which prevents it loading in Firefox 57. Is there a reason for that? You can just remove that line from the manifest and it will work on all future Firefox versions.

Blocking sites based on regexps is powerful and works well with this extension. Unfortunately it's not possible to add exceptions to a blacklist, but it can be done by negative lookahead.
I second the password protection request. Thanks.