Examine source code of OnePopup

{
  "manifest_version": 2,
  "name": "OnePopup",
  "version": "1.0",
  "description": "Gets all the opened tabs into one popup.",
  "icons": {
    "48": "icons/popup-48.png"
  },
  "permissions": [
    "<all_urls>",
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/popup-48.png",
    "default_title": "One popup",
    "default_popup": "popup/display.html"
  }
}