Can't login from local domain in Firefox

[clemdawg]

OS Name/Version: Debian 12 LXC running under Proxmox

Product Name/Version: v2.4.6.8, built 23/11/2023 12:29

Background:
I have Nginx Proxy Manager set up already on another LXC. This container handles all of my SSL certs and domain/subdomain redirections within my local network. For example: redirecting https://amp.example.lan to http://192.x.x.x:8181. I have no need at the moment to expose the AMP web portal to an actual domain that lives on the internet.

Right now I have AMP installed in an LXC with its own static IP (192.x.x.x) on my network. It was installed without HTTPS and currently resides on port 8181. My Nginx Proxy Manager container is set up to forward https://amp.example.lan to http://192.x.x.x:8181 with a self signed certificate.

What Works:
Accessing AMP from http://192.x.x.x:8181 in Firefox and Edge. I am able to login and manage AMP without issues. This is what the login page looks like.

Problem:
When accessing AMP from https://amp.example.lan using Firefox I am not able to login because the form is hidden. Inspecting the element shows form is set to display:none;

Using Edge with https://amp.example.lan seems to work just fine.

Steps to reproduce:

• Install AMP in a Debian 12 LXC with bash <(wget -qO- getamp.sh) without HTTPS on port 8181 with the static IP 192.x.x.x
• Have Nginx Proxy Manager in another container or system (would probably work on the same system) forward https://amp.example.lan to http://192.x.x.x:8181 with a self signed cert
• Access AMP from https://amp.example.lan in Firefox v120.0

Actions taken to resolve so far:

• Clearing cache, cookies, and history in Firefox
• Changing the Base URL setting in Configuration>Networking