Examine source code of Overcast.fm next

{
  "version": "1.3",
  "manifest_version": 2,
  "name": "Overcast.fm next episode button",
  "description": "adds a 'next' button to your overcast player",
  "browser_action": {
    "default_title": "overcast next button - by Thirtysix",
    "default_popup": "popup.html",
    "default_icon": {
      "300": "36.png"
    }
  },
  "icons": {
    "300": "36.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.overcast.fm/*"
      ],
      "js": [
        "inject.js"
      ],
      "all_frames": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{b9f9cbad-b0de-4ced-bc24-4735d4c8d1fb}"
    }
  }
}