Examine source code of Word Counter

{
  "manifest_version": 2,
  "name": "Word Counter",
  "version": "1.0",
  "description": "Counts the number of words on the current page.",
  "browser_action": {
    "default_popup": "counter.html",
    "default_icon": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{89033fb2-f4a0-473c-9f39-81e525c09cb9}"
    }
  },
  "permissions": [
    "activeTab"
  ]
}