Using the firewall as a web proxy.

Question

I want to configure my Sophos Firewall so that only Firefox can access the internet from a PC, and all traffic must go through the Sophos explicit web proxy (configured on port 3128). Direct HTTP/HTTPS traffic from the PC should be blocked entirely. 
 When I configure Firefox to use the proxy, web pages are blocked unless direct HTTP/HTTPS traffic (ports 80/443) from the PC to the WAN is allowed. This defeats the purpose of forcing traffic through the proxy. If I block ports 80 and 443, the proxy stops working even though traffic to port 3128 is explicitly allowed. 
 What am i missing? 
 Thanks

Erick Jan · Answer

Hi Jason, 
 Thank you for reaching out to Sophos Community. 
 Kindly try to create a firewall rule to only allow traffic via 3128, then make another firewall rule to block all (https/http) incoming traffic via port 80/443. 
 Upon applying to Firefox. Kindly check the logs viewer/monitor traffic via packet capture.