I have the exact same symptoms as TFC above. Web pages that are simple load ok, others especially those with maps, either don't load or only load partially. Disabling the web shield allows most sites to load ok, but some still don't load properly.
[for a difficult site try
http://www.dxinfocentre.com/tropo_nwe.html - this used to work fine on my machines, but hopeless since mid April]
I have 2 PCs, a desktop and a laptop, both with W7 SP0, Firefox 28, and Avast. Both show the same symptoms.
I was already wondering if my Avast set of programs had got corrupted and whether to uninstall and start again. I see there's a post earlier referring to a Windows hotfix, but it says it only applies to W7 SP1. So should I try it anyway, or if not, what else?