Examine source code of YT Capture+

{
  "name": "YT Capture+",
  "version": "1.0",
  "manifest_version": 2,
  "description": "Capture YouTube video frames with one click.",
  "permissions": [
    "activeTab",
    "scripting"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon16.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b61c425f-4451-403d-ba63-1b29784d4b29}"
    }
  }
}