Examine source code of YesPlanPlus

{
  "manifest_version": 2,
  "name": "YesPlanPlus",
  "version": "2.0",
  "description": "Adds usability features to YesPlan.",
  "icons": {
    "48": "logoN-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.yesplan.nl/*",
        "https://*.yesplan.be/*"
      ],
      "js": [
        "yesplanplus.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "yesplanplus@noctilaris.nl"
    }
  }
}