NightOwl vs OS Dark Mode: What's the Difference and Which to Use

Both NightOwl (a Firefox extension) and your operating system's dark mode settings control dark mode. They work at different layers and affect different things. Here is a clear comparison.

What OS dark mode does

macOS, Windows, and Linux all have a system-level dark mode setting. When you enable it:

• The OS interface switches to dark colors (menus, windows, system apps)
• Applications that follow the system setting switch to dark mode
• Websites that implement prefers-color-scheme: dark in their CSS will switch to dark mode

What it does NOT do: Force dark mode on websites that have not implemented it. Many websites — news sites, older web apps, legacy enterprise tools — do not check prefers-color-scheme and will stay light even when your OS is in dark mode.

What NightOwl does

NightOwl is a Firefox extension that injects CSS into every page to force dark mode, regardless of whether the site implements prefers-color-scheme.

When NightOwl is active:

• Every website you visit is displayed in dark mode
• Sites that do not natively support dark mode get the extension's dark treatment
• You can whitelist specific sites where you want to preserve the light display

What it does NOT do: Affect the OS interface, desktop apps, or anything outside Firefox.

Side-by-side comparison

Which to use

Use OS dark mode for system-wide dark interface (apps, menus, file manager).

Use NightOwl for forcing dark mode on websites that do not implement it natively.

Use both for a comprehensive dark experience: OS dark mode handles everything outside the browser; NightOwl handles websites inside Firefox.

They do not conflict — they affect different layers.

Install NightOwl for Firefox

NightOwl is one of 11 Firefox extensions I built — see the full series.