Install Squid built with SSL decryption support
Login to Web UI and select System / Package Manager / Available Packages , find and install package squid.
Wait until squid package is installed.
After successful installation goto Services / Squid Proxy Server, select Local Cache tab, scroll all the way down and click Save.
Now select General tab, set the Enable Squid checkbox, select both LAN and loopback interfaces for Squid to bind to, scroll all the way down and click Save.
Reboot your pfSense box now. After reboot, login to Web UI, select Status / Services. The green checkbox on the right will indicate Squid service is up and running.
Now adjust your browser configuration to point to pfSense box and try browsing the web. Squid is now working.