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).