[https://imgur.com/a/QQRu6K7 You can see below] my choices for - [https://support.mozilla.org/en-US/questions/1360536#answer-1465159 `1` for light, in `layout.css.prefers-color-scheme.content-override` ] - [https://support.mozilla.org/en-US/questions/1359881#answer-1465837 `0` for light, in `ui.systemUsesDarkTheme`]. - [https://support.mozilla.org/bm/questions/1366505#answer-1479986 "Light" website appearance AND theme](). '''But why some websites still darken and blacken background ? Examples are https://superuser.com, https://softwarerecs.stackexchange.com.''' This mishap DOESN'T happen in Troubleshoot Mode. But I don't have the [https://addons.mozilla.org/en-US/firefox/addon/darkreader/ Dark Reader extension]. [https://superuser.com/q/1821906 ''Cross-site Backup'']