FortiGate 100E webfilter SSL certificate error

Hi there,

I am trying to configure webfilter in ForitGate 100E: the filter is up and running, but I have different behaviors in browsers.

This is the filter configuration:

For Edge/IE browser, when a site is filtered, I can view the FortiGate page correctly, in Firefox browser I get the error "secure connection failed" and FotriGate page are not shown, in Chrome browser instead I get error "Connection it is not private" NET:ERR_CERT_INVALID and FortiGate page are not shown.

Can anyone help me to make correct configuration to make all browsers able to show FortiGate webfilter page?

Thank in advance.

Very kind regards.

Alessio