Examine source code of Google Keep button

{
  "manifest_version": 2,
  "name": "Google Keep",
  "version": "1.0",
  "description": "Google Keep button",
  "background": {
    "scripts": [
      "button.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{2bb5be57-7c0f-44c1-95c1-9cf92623d40d}"
    }
  }
}