mitmproxy/doc-src/certinstall/firefox.html

How to install the __mitmproxy__ certificate authority in Firefox:

<ol>
    <li> If needed, copy the ~/.mitmproxy/mitmproxy-ca-cert.pem file to the target. </li>

    <li>Open preferences, click on "Advanced", then select"Encryption":
        <img src="@!urlTo('firefox3.jpg')!@"/>
    </li>

    <li> Click "View Certificates", "Import", and select the certificate file: 
        <img src="@!urlTo('firefox3-import.jpg')!@"/>
    </li>

    <li>Tick "Trust this CS to identify web sites", and click "Ok":
        <img src="@!urlTo('firefox3-trust.jpg')!@"/>
    </li>

    <li> You should now see the mitmproxy certificate listed in the Authorities
    tab.</li>

</ol>