I'm not sure how privoxy works, so I don't know if this will work.
Open the avastUI, Settings, Troubleshooting section, Redirect Settings, WEB, HTTP port(s)add the privoxy port after the 80, e.g. 80,8118 where 8118 is the privoxy port (you will need to confirm that privoxy port) and uncheck the Ignore local communication, see image example.