Doesn't work on Mac and Windows

[gkns]

When I set Firefox browser to point to this proxy and try to access an HTTPS-enabled site, I get an error from the browser:

"Failed to establish a secure connection"

I tried to reach an HTTPS website through a Python requests client as well but to no avail.
The certificate was generated using the command:

openssl req -new -x509 -keyout localhost.pem -out localhost.pem -days 365 -nodes

Also this certificate was added to the Firefox trust Authorities.

The issue has been observer on both Mac Mojave and Windows 10, with Python 3 and OpenSSL versions: OpenSSL 1.1.1c 28 May 2019 and OpenSSL 1.1.1g 21 Apr 2020