As others have pointed, it is a fake. It doesn't block anything, it allows the listed Pages to load, then redirects them to a blank Page, also cleaning the address bar. If the Page is lightweight, one may not notice that happening, but loading heavy Pages easily shows the fraud. And no, it's not a cache problem or whatever, as I cleared everything before testing. Also, the BACK button becomes active, so it's even possible to go back to the supposedly blocked Page (what will redirect to the blank Page again, but the wasted bandwidth, system memory, time and whatnot will still happen). Someone should take this trashy add-on down!
I've been looking for something to block sites for about a whole week, and just found hyped complements with unique features, international approve and other bs they say to gather attention. Until I found this. It's simple and not glitched, could be improved slightly like with an addition of website redirection or complete block, but remains the best beyond others at getting its job done.
I did the same thing as a previous user. Signed up so I could write a review. When ever I would click on one of those sites to read about interesting thing or pictures a bunch of trash windows would open up and things would slow down. This app stopped that from happening and the site I wanted to see loaded with lightning speed compared to before. Don't know how it will work when a bank will redirect me to a login page but it will be worth the effort to use it for sites like iTorrentz that load a bunch of add pages if you click on any of their links. 4-stars because there is always room for improvement.
I just loaded this add-on and specified several sites and none of them have been blocked after several restarts of Firefox. The doc that shows up in the Option pop-up is truncated thus it whole Whitelist discussion is lost. I loaded another add-on on my wife's XP machine that works great - wish I could find it again!