Hello there !
First post and after reading a few, I'd like to share with you how to seamless integrate Indigo SSL into your beloved Firefox.
During initialization, Indigo registers a certificate authority in your mac keychain.
Just open your keychain app, open the system keychain and open the certificate tab. You'll find a certificate named mkcert. Click on it and then file/export, chose PEM format (I didn't test with the other formats, maybe it would work).
Then on Firefox, go to parameters, privacy and security and at the very end of the long page, click on view certificates. Then chose the Authorities tab and click on import. Import your file and Voila !
No more https errors 🙂