to be specific, go to the Avast interface, click settings, from there you will see 'Web Shield', turn that SOB off and you'll be transported back to the 21st century. If that doesn't work try the Flux Capacitor.
Actually try this, I think it's better than turning your web shield off.
I followed this suggestion found on this thread: http://forum.avast.com/index.php?topic=120600.0, and had the issue fixed. Do this:
avast! GUI -> Security -> Web Shield -> Settings -> Main Settings
Enable: Scan traffic from well-known browser processes only
Enabling this doesn't make avast! any less secure from what I've read.