Apparently there is a brand new Web Standard now for making Browsers able to request Dark Mode Versions of Websites.
And since it is new, its not publicly supported by the Browsers yet in most cases.
But latest Firefox can already handle it with some about:config changes:
ui.systemUsesDarkTheme = 1 (may require you to actually make a new integer field)
browser.in-content.dark-mode = true
privacy.resistFingerprinting = false (Unsure if it’s a Firefox Bug or a Feature, but resisting Fingerprinting causes Dark Mode to fail, since requesting Dark Mode does help Sites with Fingerprinting)
While we are at it, here is some good security Advice for Browsers. ;)
Yes, I am very aware about how often I share a link to this Page, what makes it kinda non-secret. The only way to find this, aside from me telling it in some random Chat, is by reading the Changelog of GT6, where it is mentioned at the very bottom of the Page.
This Version is exclusively for Testing purposes and absolutely UNPLAYABLE, the Download yields whatever work in progress I have, which might be very savegame breaking or even crashing on startup. Please wait for the official Releases, that should be less than a week of waiting. Do not report Bugs inside this Version unless I explicitely ask you personally to do so. I usually didn’t even test that Version myself as it gets built the same moment my script puts it into my Mods Folder to start MC.