[EDITED] Settings page is blank due to mixed content

Hello.
I'm using 6.1.1 (build fc853b) – May 31, 2017 on Ubuntu Server 16.04. Until yesterday, everything was working smoothly, but today, Settings page is blank. I can not see anything unusual in the log. Any help/advice?
Problem:

Excerpt of log file:
EDIT:
Apparently, the problem is caused by non-secure http content within settings page. I'm using nginx + certbot to redirect incoming connections to my subsonic (https from outside redirected to a standard installation without enabling https in the local network). I'd appreciate any advice here. Disabling protection for mixed content in Firefox "works", but is not ideal.
I'm using 6.1.1 (build fc853b) – May 31, 2017 on Ubuntu Server 16.04. Until yesterday, everything was working smoothly, but today, Settings page is blank. I can not see anything unusual in the log. Any help/advice?
Problem:

Excerpt of log file:
- Code: Select all
[7/27/17 11:51:24 AM CEST] INFO HsqlDaoHelper Checking database schema.
[7/27/17 11:51:24 AM CEST] INFO HsqlDaoHelper Done checking database schema.
[7/27/17 11:51:24 AM CEST] INFO SettingsService Java: 1.8.0_131, OS: Linux
[7/27/17 11:51:24 AM CEST] INFO VersionService Resolved local Subsonic version to: 6.1.1
[7/27/17 11:51:25 AM CEST] INFO MediaScannerService Automatic media library scanning scheduled to run every 1 day(s), starting at Fri Jul 28 03:00:00 CEST 2017
[7/27/17 11:51:25 AM CEST] INFO UPnPService Starting UPnP service...
[7/27/17 11:51:25 AM CEST] INFO PodcastService Automatic Podcast update scheduled to run every 24 hour(s), starting at Thu Jul 27 11:56:25 CEST 2017
[7/27/17 11:51:25 AM CEST] INFO UPnPService Disabling UPnP/DLNA media server
[7/27/17 11:51:25 AM CEST] INFO UPnPService Starting UPnP service - Done!
[7/27/17 11:51:35 AM CEST] WARN NetworkService No UPnP router found.
[7/27/17 11:53:10 AM CEST] INFO BootstrapVerificationFilter Servlet container: jetty-6.1.x
[7/27/17 11:53:10 AM CEST] INFO VersionService Resolved latest Subsonic final version to: 6.1.1
[7/27/17 11:53:10 AM CEST] INFO VersionService
EDIT:
Apparently, the problem is caused by non-secure http content within settings page. I'm using nginx + certbot to redirect incoming connections to my subsonic (https from outside redirected to a standard installation without enabling https in the local network). I'd appreciate any advice here. Disabling protection for mixed content in Firefox "works", but is not ideal.