Then why post the link which is about the webrep as that has nothing to do with the Site Blocking feature and is different to your problem. See image1 test using firefox 3.6.13.
You saying the site blocking doesn't work with Opera, because it isn't displaying that image which is different again.
This may also be an Opera issue, I don't know as I don't use it, but the image that is displayed is on your system (localhost) and is inserted into the displayed page, image2. So there may be something in Opera blocking that image as the rest of the page html is there.