Examine source code of Knack Utils

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  "manifest_version": 2,
  "name": "Knack Utils",
  "short_name": "Knack Utils",
  "description": "Useful utilities for the Knack.com Builder",
  "content_scripts": [
    {
      "matches": [
        "https://builder.knack.com/*/*"
      ],
      "js": [
        "inject.js"
      ],
      "all_frames": true
    }
  ],
  "icons": {
    "128": "assets/images/logo.png"
  },
  "web_accessible_resources": [
    "assets/**",
    "content.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "knack-utils@icewolf.ca"
    }
  }
}