You could try Firefox's "Website appearance" settings, to inform compatible websites to use dark mode: [[Change website appearance settings in Firefox]] But many sites don't switch based on your browser's preference, so you can use an add-on to modify the colors. This one is popular: * Dark Reader: https://addons.mozilla.org/firefox/addon/darkreader/ * It is in the [[Recommended Extensions program]] It slows things down just a little bit, but it's usually worth it. Let us know what you think.

Sorry, for Android, the settings are different. I think you would start by selecting the Dark theme: [[Using Dark Theme in Firefox for Android]].