Worked fine for me. I don't know what others are talking about, maybe the problem was during update, or they're stupid.
-2 star because it blocks the site in the URL, After you've clicked on it. The website is added to firefox's history, including the back button. Which causes the back button to loop. I assume(not tested) that it would fail to block the site if it were embedded in another.
I expected this blocker to remove and/or disable links in all active html/pages I was viewing. I need a PRE-blocker, not a POST-blocker.