HTTP Proxy Refusing Connections from LAN devices

[NoX1De]

I have Gluetun running in a docker container and have exposed tcp/8888 as per the documentation, however whenever I configure a LAN device's browser (This only happens in Firefox) to use my docker host's IP and tcp/8888 as it's HTTP/S proxy it repeatedly refuses connections with the error NS_ERROR_PROXY_CONNECTION_REFUSED, when I nmap my docker host on tcp/8888 with a simple TCP connect single port scan it reports as open and responding w/ a SYN-ACK....sooo kind miffed here. I have FIREWALL_OUTBOUND_SUBNETS configured for my entire home network /24...any ideas?

[NoX1De]

This issues seems to be isolated to Firefox...I've seen some things searching around trying to solve this that are hinting at that this may be a CORS issue with local http->https proxying but disabling CORS in Firefox in about:config didn't change anything. No idea what is causing this, proxying connections through gluetun's http proxy with other browsers works just fine.