Hello there. I have noticed that when Avast's web shield is enabled, it will block access to certain sites. Not all, though. Now this wouldn't be a problem if it were blocking access to bad sites, that would be a good thing. However, when it is active it will block many legitimate sites from being accessed.
These include the avast forums, the mozilla addons site, some reading sites, and some others I can't quite remember at the present time. Avast doesn't give any sort of notification when this happens, so I assume it is a bug of sorts.
Any help would be appreciated, I have turned off Avast's web shield for the time being as a workaround.