To deploy Firefox customizations on macOS:

Step 1: Install Firefox

1. Download Firefox and then open the disk image.
2. Drag the Firefox application onto your desktop or some other location so that you can modify it.

Step 2: Remove quarantine set by macOS

Before you modify any files in the Firefox application, you must remove the quarantine that macOS sets by default for applications downloaded from the Internet. To do this, run the following command from a Terminal:

xattr -r -d com.apple.quarantine Firefox.app

If you see an error on startup that says:

Firefox is damaged and can’t be opened. You should move it to the Trash.

This means that you did not run this command.

Step 3: Deploy customizations

Deploy customizations made with policies.json

If you want to deploy customizations that were made with policies.json, create a directory called distribution in the Contents/Resources directory and place the policies.json file into that directory.

Deploy customizations made with Autoconfig

If you want to deploy customizations that were made with AutoConfig, place the autoconfig.js file into the Contents/Resources/defaults/pref directory and the firefox.cfg file into the Contents/Resources directory.

Once you have made the changes that you need, you can deploy the customized Firefox.app file.