Examine source code of Watch Later Feed

{
  "manifest_version": 2,
  "name": "Watch Later Feed",
  "description": "Make your YouTube feed show only Watch Later videos",
  "version": "1.1.8",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "128": "icon/128.png"
  },
  "permissions": [
    "activeTab",
    "scripting",
    "storage",
    "unlimitedStorage",
    "declarativeNetRequest",
    "*://*.youtube.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "watchlaterfeed@notstoneroller.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "web_accessible_resources": [
    "watch-main-world.js",
    "yt-main-world.js"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Watch Later Feed Settings",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*",
        "*://youtube.com/*"
      ],
      "run_at": "document_end",
      "css": [
        "content-scripts/content.css"
      ],
      "js": [
        "content-scripts/content.js"
      ]
    }
  ]
}