It took me a while to figure this out:
After installing Avast Free 6, I can't go anywhere in FireFox or IE. Firewall shut off completely.
I eventually disabled the Web Shield, and now I can get out to the Internet. Uninstalled and re-install Avast, no good, problem is still there. So, for now, I just have to leave Web Shield disabled.
With the Web Shield enabled, web sites eventually time out. In IE, after a while, it offers to do Diags, and HTTP/HTTPS and FTP all fail.
Is this a known issue?