NightOwl is a Firefox extension that automatically applies dark mode to every website based on your local sunset and sunrise times. Here is how to set it up.
Install
Go to NightOwl on Firefox Add-ons and click "Add to Firefox."
Step 1: Set your location
After installation, click the NightOwl icon in the Firefox toolbar.
You will see a location field. Enter your city name (e.g., "New York" or "London") or your coordinates.
NightOwl uses this to calculate local sunset and sunrise times. It makes no ongoing network requests — the sunset calculation is done mathematically.
Step 2: Choose your mode
Auto (sunset/sunrise): Dark mode turns on automatically at sunset and off at sunrise. This is the recommended setting — you set it once and never touch it again.
Schedule: Dark mode turns on and off at hours you specify (e.g., 8 PM to 7 AM). Use this if you prefer a fixed schedule over astronomical timing.
Always on: Dark mode is always active.
Always off: Dark mode is disabled (temporarily pause if needed).
Step 3: Configure site exclusions
Some websites implement their own dark mode and may conflict with NightOwl's CSS injection. For these sites, add them to the exclusion list.
Click the NightOwl icon → Settings → Excluded Sites → add the site URL.
Common sites to exclude: Google services (Gmail, Google Docs), sites with their own well-implemented dark mode.
Verifying it works
Wait until your local sunset time. All websites should switch to dark mode. If a site does not switch, it may be using CSS that overrides the extension's injection — add it to the exclusion list.
Resetting settings
If you change cities or move timezones, update your location in the NightOwl settings. The sunset/sunrise times will recalculate immediately.
NightOwl is one of 11 Firefox extensions I built — see the full series.
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