thanks EricJH & panic for answering my question.
edited for privacy… sorry.
You want to block all outgoing and incoming traffic on all ports except port 80? And only allow for HTTP traffic? Is that correctly understood?
You would need to set up a global firewall rule that blocks all ports outbound, but with exceptions for ports 80 (HTTP), 443 (HTTPS) and 53 (DNS).
Ewen 