How to enable Firefox's dark theme on any operating system ( Windows 10, Chrome, Safari)

Firefox has respected Windows 10’s dark mode setting now. But you can manually enable dark mode in Firefox, on any operating system.
To change your page’s theme,click the menu button (three horizontal lines) in the top right, then go to “Add-ons and themes” in the drop-down menu.
Click “Themes” .
The Dark theme is Firefly’s dark mode. Everything in Firefox will turn black or a dark shade of gray with the dark theme.
To enable the Dark theme click the “Enable” button to the right of it.
The default Firefox dark theme is elegant and minimalist, but if you’re looking for something more specific.