Same problem here with WAMP and Joomla! while AIS 14 Firewall is active.
Meanwhile got these instructions twice from Avast:

Hello, try this: 1) Go to "Settings" 2) Go to "Troubleshooting" 3) Expand "Redirect Settings" 4) Under "WEB" look for ignored address 5) Add localhost 6) Open browser and visit your localhost page.

Doesn’t work and doesn’t make to much sense.
This is my first major problem with AVAST and I don’t like the way they deal with such a problem.
Regards … Franz