Examine source code of MBs Tab Volume Control

{
  "manifest_version": 2,
  "name": "Tab Volume Control",
  "version": "1.0",
  "description": "Adjust the volume of individual browser tabs",
  "permissions": [
    "tabs",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup/popup.html",
    "default_title": "Tab Volume Control",
    "default_icon": {
      "48": "icons/icon.svg",
      "96": "icons/icon.svg"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_scripts/inject.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    },
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_scripts/volume-control.js"
      ],
      "run_at": "document_end",
      "all_frames": true
    }
  ],
  "icons": {
    "48": "icons/icon.svg",
    "96": "icons/icon.svg"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "tab-volume-control@addon",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}