Examine source code of Amazon No Fake

{
  "manifest_version": 2,
  "name": "Amazon No Fake",
  "description": "Amazon商品ページにFakespotのレビューとKeepaの価格遷移を表示する拡張機能です。",
  "version": "4.0.0",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "96": "icon/96.png",
    "128": "icon/128.png"
  },
  "permissions": [
    "storage",
    "scripting",
    "system.display",
    "*://*.amazon.co.jp/*",
    "https://sakura-checker.jp/*",
    "*://*.fakespot.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Default Popup Title",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.amazon.co.jp/*"
      ],
      "run_at": "document_end",
      "js": [
        "content-scripts/content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{3f6fb0da-ef0b-4253-a2b2-592181615f2c}"
    }
  }
}