Examine source code of Tab Volume Manager

{
  "manifest_version": 3,
  "name": "Tab Volume Slider",
  "browser_specific_settings": {
    "gecko": {
      "id": "tab-volume-slider@nbili",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "version": "1.1",
  "description": "Per-tab volume control with boost",
  "permissions": [
    "menus",
    "tabs"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "inject.js"
      ],
      "all_frames": true,
      "run_at": "document_start",
      "world": "MAIN"
    },
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "all_frames": true,
      "run_at": "document_idle"
    }
  ],
  "action": {
    "default_popup": "popup/popup.html",
    "default_icon": {
      "16": "icons/icon-16.svg",
      "48": "icons/icon-48.svg",
      "128": "icons/icon-128.svg"
    }
  },
  "icons": {
    "16": "icons/icon-16.svg",
    "48": "icons/icon-48.svg",
    "128": "icons/icon-128.svg"
  }
}