I have some websites blocked in my hosts file, and FF 4 would display an error message when I would try to go to one of the blocked web sites. Firefox 5 does not display an error message when one of these blocked sites is accessed, it only displays a blank page. I tried a Stylish add-on for about:blank, but that does not work, either. I would like to see the error message come back to me, so I can at least know what happened. Even if I try to load a page that is not blocked in my hosts file, and perhaps that particular website is down, I would not know anything about it!