Cannot be displayed correctly via https

Hi,

just tried to access *https://talkingkotlin.com/* (with firefox 54.0) and encountered two issues:
1. Certificate is not being trusted 
2. resources are catched via http, which is considered insecure and bad practise: https://support.mozilla.org/en-US/kb/mixed-content-blocking-firefox?redirectlocale=en-US&redirectslug=how-does-content-isnt-secure-affect-my-safety

kind regards