Title: Enable dark mode on Firefox
       Author: Solène
       Date: 04 May 2020
       Tags: firefox
       Description: 
       
       Some websites (like this one) now offers two differents themes: light
       and dark.
       
       Dark themes are proven to be better for the eyes and reduce battery
       usage on
       mobiles devices because it requires less light to be displayed hence it
       requires less energy to display. The gain is optimal on OLED devices
       but it
       also works on classic LCD screens.
       
       While on Windows and MacOS there is a global setting for the user
       interface in
       which you choose if your system is in light or dark mode, with that
       setting
       being used by lot of applications supporting dark/light themes, on
       Linux and
       BSDs (and others) operating systems there is no such settings and your
       web
       browser will keep displaying the light theme all the time.
       
       Hopefully, it can be fixed in firefox as [as explained in the
       documentation](https://developer.mozilla.org/en-US/docs/Web/CSS/@media/
       prefers-color-scheme).
       
       To make it short, in the about:config special Firefox page, one can
       create a
       new key `ui.systemUsesDarkTheme` with a number value of `1`, the
       firefox
       about:config page should turn dark immediately and then Firefox will
       try to use
       dark themes when they are available.
       
       You should note that as explained in the mozilla documentation, if you
       have the
       key `privacy.resistFingerprinting` set to `true` the dark mode can't be
       used.
       It seems dark mode and privacy can't belong together for some reasons.
       
       Many thanks to
       [https://tilde.zone/@andinus](https://tilde.zone/@andinus) who
       pointed me this out after I overlooked that page and searched a long
       time with
       no result how to make Firefox display website using the dark theme.