Examine source code of Visits Counter

{
  "author": "igorlogius",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "128": "icon.png"
  },
  "manifest_version": 2,
  "name": "visits-counter",
  "browser_action": {
    "default_area": "navbar",
    "default_popup": "popup.html"
  },
  "permissions": [
    "tabs",
    "history",
    "storage"
  ],
  "options_ui": {
    "page": "options.html"
  },
  "description": "Indicates how often the open website has been visited before, by showing a visited counter on the toolbar icon and also adds some timestamped wayback links",
  "optional_permissions": [
    "notifications"
  ],
  "version": "1.4.4",
  "browser_specific_settings": {
    "gecko": {
      "id": "{90052e28-eb23-41ed-be98-1d0fe403a7a3}"
    }
  }
}