Windows 7
How to install the mitmproxy certificate authority in Windows 7:
1: Copy the ~/.mitmproxy/mitmproxy-ca-cert.p12 file to the target system.
2: Double-click the certificate file. You should see a certificate import wizard:

3: Click "Next" until you're prompted for the certificate store:

4: Select "Place all certificates in the following store", and select "Trusted Root Certification Authorities":

5: Click "Next" and "Finish".