https://www.bleepingcomputer.com/news/software/firefox-for-ios-update-brings-a-dark-theme-and-searchable-tabs/

A new update for Firefox for iOS has been released that now offers a dark theme for those who do not wish to disturb others who are sleeping or feel it is easier on their eyes. Also included in this update is the ability to search and reorder your open tabs.

While Firefox already included a Night Mode, which caused web sites that you visit to have a dark background and white, or lighter colored text, the app itself still retained its normal colors. With this new version, Firefox now has an actual dark theme that converts the app itself to use a dark background with lighter text.