Unfortunately it doesn't work as I hoped.

My expectation - in addition to blocking possibly a particular site - is mainly to hide unwanted and blacklisted sites on BlockSite from search results.

Just like Personal Blocklist on Chrome does.
(the same Personal Blocklist for Firefox, by a different author, doesn't work either.)

Works just fine. However, I strongly dislike how it appears when one goes to a site one has blocked. It looks like you've been taken to some hack site. It would be MUCH BETTER if instead of the page heading being "Restricted Access" it said something like "This page/site has been block by the Block Site Firefox Addon."
Please, don't expect me to realize what is going on by seeing some stupid icon either. (I hate icons, but they're here to stay.) Secondly--although this may be an option--the screenshot shown in the example is white, while I get a BLACK screen (which, again, looks hackish).

A little quirky but does what it needs to do. I have a semi-issue where it doesn't remember that I've paused blocking when closing and reopening the firefox. It's kind of obnoxious so I might make an Issue on Github. A quicker path than going through the FF extensions manager to the config page would be nice as well. Some improved documentation on redirecting would be nice.

It does not block sites by URL, it actually has a totally different function from the name.

Good idea but this extension needs stronger security. My 11 year old son simply disabled the extension to get to the blocked website (Youtube). Aside from requiring a password to remove a website, the password should also be needed to allow (or disallow) a user from simply disabling the extension. Looking forward to a fixed extension with stronger security features.