Examine source code of Spoiler Free VBTV

{
  "manifest_version": 2,
  "name": "Spoiler Free Volleyball World TV",
  "version": "1.2",
  "description": "Removes spoilers when browsing replays on Volleyball World TV",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://tv.volleyballworld.com/*"
      ],
      "js": [
        "remove_spoilers.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{7380d393-d67a-4068-986d-0c2a77d0aee8}"
    }
  }
}