1. Go to about:config and enable toolkit.legacyUserProfileCustomizations.stylesheets.

2. Locate your profile location by going to about:support and clicking Open folder in Profile folder.

3. Clone this repository by running git clone https://github.com/synthicy/nightfox.

4. Paste the chrome folder into the correct profile folder.

For the blur style to work enable layout.css.backdrop-filter.enabled in about:config.

5. Copy these customization settings to get the exact spacing and look you see in the preview. You can use the Flexible Spaces for the gaps.

Want to get this DuckDuckGo theme? Go to https://duckduckgo.com/settings#theme and enter the password nightfall.

Nightfox is based off of: https://github.com/datguypiko/Firefox-Mod-Blur