Examine source code of Appoint.ly

{
  "name": "Appoint.ly",
  "description": "Extracting appointments links",
  "version": "1.2resigned1",
  "manifest_version": 2,
  "browser_action": {
    "default_popup": "extension.html",
    "default_icon": "icons/Appointly_icon.png"
  },
  "permissions": [
    "tabs",
    "https://appoint.ly/*",
    "cookies"
  ],
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Ctrl+Shift+F",
        "mac": "MacCtrl+Shift+F"
      },
      "description": "Opens hello.html"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{daa42b3e-d48d-4db6-b6f3-08b1968c4d74}"
    }
  }
}