soundy plug in problem on HTTPS

Hi, got recently onto HTTPS with the Better Search Replace Plug in. Needed a debug howver since the site showed a green lock symbol at the address line with a grey shield (You’ll see a green lock with a grey warning triangle when Firefox has blocked any insecure elements on the page. This means that the page is now secure).
I changed out the sound files on the soundy plug in V. 3.61. The sound files had an internal HTTP address upon upload, but seeking to change those to HTTPS did not worrk/did not handle the issue.
Once I disactivated the plug in the grey shield was disappeared and the lock was green
Any data on what could handle the issues would be great.