avast doesn't selectively block URL unless you have put them in the URL Blocking section of the Web Shield, so if it is able to browse other sites, a) the web shield is working and b) the firewall isn't blocking the web shield.
So by blocks what exactly do you see, a web page with error 404, etc. what ?
Besides that I can view that site with firefox, so it is working for me with avast web shield and firefox.
Have you tried a different browser ?