NightOwl for Firefox: Force Dark Mode on Any Website

You have your OS set to dark mode. Firefox follows that preference. But then you visit a documentation site, a forum, or a corporate intranet, and — blinding white screen.

Those sites either don't implement prefers-color-scheme, or they implement it incorrectly. You can't fix their CSS, but you can override it.

What NightOwl Does

NightOwl is a Firefox extension that injects a CSS dark mode override on any page you choose. It works by:

1. Applying a high-specificity CSS inversion to the entire page
2. Re-inverting images and media (so photos look normal)
3. Remembering your per-site choice in browser.storage.local

It doesn't use any AI, cloud calls, or external services. Everything runs locally.

Who It's For

• OLED screen users who want to preserve battery and protect display longevity
• People with light sensitivity who need dark backgrounds regardless of site design
• Night-mode enthusiasts who don't want to manage exceptions manually

How It Compares

Most "dark mode everywhere" solutions fall into two categories:

Browser-level forced dark mode (like Firefox's experimental setting): Rewrites the entire page, often breaking layouts. It's an all-or-nothing switch.

Site-specific extensions (like NightOwl): You toggle per domain. Sites that already look good in dark mode stay untouched. Only the stubborn ones get overridden.

Usage

After installing, click the NightOwl icon on any page to toggle dark mode for that domain. Your preference is saved — next time you visit, it remembers.

The extension has no account, no permissions beyond the current tab, and no network calls.

---

Install it: addons.mozilla.org/en-US/firefox/addon/nightowl1/

If you have sites that perpetually ignore your dark preference, this handles it in two clicks.