Examine source code of Word Counter v3

{
  "manifest_version": 2,
  "name": "Word Counter",
  "version": "1.0",
  "description": "Count the number of words on a webpage or in a selected text.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{06cd5a3f-63b7-4362-a62f-c8f9b5013de1}"
    }
  }
}