The most common way to enable dark mode in Firefox is manually: click a toggle, switch between light and dark. This works but requires you to remember to do it.
Here is how to have Firefox switch dark mode automatically.
Option 1: Use NightOwl (automatic by sunset)
NightOwl is a Firefox extension that applies dark mode automatically based on your location's sunset and sunrise. When sunset occurs, dark mode turns on. At sunrise, it turns off.
Setup:
- Install from Firefox Add-ons
- Open the extension popup
- Set your location (city name or coordinates)
- Choose "auto sunset/sunrise" mode
After setup: nothing else required. Dark mode turns on and off automatically every day.
Customization: If you prefer a fixed schedule (e.g., dark mode from 8 PM to 7 AM), you can set that instead of using astronomical sunset/sunrise.
Option 2: Follow your OS dark mode setting
Firefox can follow your operating system's dark mode setting:
- Open
about:configin Firefox - Search for
ui.systemUsesDarkTheme - Set it to
1(always dark mode in Firefox UI)
Or, install a theme from Firefox Add-ons that follows the system setting automatically.
Limitation: This controls the Firefox interface (toolbars, tabs), not website content. Websites themselves need to implement prefers-color-scheme: dark for their content to switch automatically.
Option 3: NightOwl with specific schedule
For users who do not want sunset-based switching:
- Install NightOwl
- Open settings
- Choose "Schedule" mode
- Set specific hours (e.g., 20:00 to 07:00)
Dark mode turns on at 8 PM and off at 7 AM every day. No manual toggle.
Which to use
- Want sunset/sunrise tracking: NightOwl with auto mode
- Want specific hours: NightOwl with schedule mode
- Want Firefox UI only (not websites): System setting + Firefox about:config
For most users who want websites to display in dark mode automatically, NightOwl is the most direct solution.
NightOwl is one of 11 Firefox extensions I built — see the full series.
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