Examine source code of Yarn Ball

{
  "manifest_version": 2,
  "name": "Yarn Ball",
  "author": "Joseph Duffy",
  "icons": {
    "32": "assets/icon-32.png",
    "48": "assets/icon-48.png",
    "64": "assets/icon-64.png",
    "96": "assets/icon-96.png",
    "128": "assets/icon-128.png",
    "256": "assets/icon-256.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "exclude_matches": [
        "*://yarnpkg.com/*"
      ],
      "js": [
        "background.js"
      ],
      "run_at": "document_start"
    }
  ],
  "description": "Replace npm commands on web pages with their yarn equivalent",
  "version": "1.0.1resigned1",
  "browser_specific_settings": {
    "gecko": {
      "id": "{846e8cdc-61c1-4bab-a3ec-4e84c8b108b2}"
    }
  }
}