So a full MITM like Privoxy with access to the browser TLS handshake can not obtain or access or alter or replace the certs needed to decrypt web browser traffi

So a full MITM like Privoxy with access to the browser TLS handshake can not obtain or access or alter or replace the certs needed to decrypt web browser traffic? In other words, it's not possible for MITM (like Privoxy) to operate in a transparent manner.