Examine source code of Mustache icon

{
  "manifest_version": 2,
  "name": "Mustache icon",
  "version": "1.0",
  "description": "The mustache symbol is a familiar image, carrying many different meanings depending on the context from humorous, classic to men's fashion or barber brand.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html",
    "default_title": "Click me!"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{305d5e2a-03a1-4a62-9854-8be28a1fcfc3}"
    }
  }
}