Examine source code of Auto Refresh Premium

{
  "manifest_version": 2,
  "name": "Word Counter",
  "version": "1.0",
  "description": "Count words and characters on a web page.",
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "word_counter@addon.dev"
    }
  }
}