Firefox 78 or higher - Enable Dark Mode in UI, Bookmarks, Options

If you're a Firefox browser user, here's a quick tip on how to enable Dark Mode in Firefox UI, Bookmarks/Library and Options pages.

1. Type about:config in the address bar.
2. Accept the warning to continue.
3. In the search bar at the top, type:  ui.systemUsesDarkTheme
4. Click the "Number" radio button, then click the "+" icon to create a new preference.
   Enter the value: 1  (0=light; 1=dark; 2=no preference)
5. Click the V to confirm.

The change is immediate. Your eyes will thank you. 

Cheers :-)