If after installing the certificate you still get the message "Your connection to this site is not fully secure".
This typically happens when a website shares mixed content. This means there is both secure and non-secure content (HTTPS and HTTP) being delivered over SSL to your browser.
This test will help you to find out if you're affected: https://gf.dev/mixed-content-test
Once you runt the test, you will see the content that is being loaded over HTTPS