Hi, try to delete WebShieldSgn.htm (C:\Program Files\AVAST Software\Avast\1033\WebShieldSgn.htm). To ensure that the file will not be restored in a future, create folder with the same name.
To do it, you must disable Avast self-defense - Avast UI / Settings / Troubleshooting / Enable Avast self-defense module must be unchecked. Don't forgot to enable the self-defense again after creating the folder.