This could be the issue: https://security.stackexchange.com/a/163200

Thanks for the reply.

Unfortuntely that didnt work.

I added as a p12 but no joy. Accepts password ok but I still get insecure message.

Any other ideas? Thanks.

Ah, I think you made the same mistake as the other guy in the question: you are trying to install a server certificate as a client cert, which won't work.

If you follow the guide from here: https://tommcfarlin.com/enable-ssl-in-mamp/ You should find, that it shows the self-signed certificate warning instead of this one, and you can simply add an exception.

Thanks for your rely.

The Mamp SSL works perfectly in Chrome and Safari though. It's just in Firefox that theres an issue.

Exceptions kind of work but i still get an insecure message in firefox but not in other browsers.

Maybe I don't see, what are you doing exactly. Is this a self-signed key or not? Is Chrome working without any user interaction? What happens when Firefox connects without setting any cert related thing?