Examine source code of Calendar icon

{
  "manifest_version": 2,
  "name": "Calendar icon",
  "version": "1.0",
  "description": "Icons are commonly used in applications to represent: Schedule events, View dates, Set appointments, Reminders.",
  "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": "{914dcdb6-6307-46b5-9325-65f8f59adda2}"
    }
  }
}