Lightweight dark mode extension for Firefox that works via CSS inversion rather than JavaScript injection.

Why that distinction matters for privacy-minded users: extensions that inject JS into pages can read page content, intercept form data, etc. NightOwl applies a CSS filter at the browser level — the page itself doesn’t know the extension is running.

It’s not as feature-rich as Dark Reader (no per-site configuration, no brightness adjustments), but it’s simpler and doesn’t touch page content.

Source is available if you want to review what it does.