Examine source code of SmartTabSound

{
  "manifest_version": 2,
  "name": "SmartTabSound",
  "version": "1.0.0",
  "description": "Control audio volume independently for each browser tab",
  "permissions": [
    "tabs",
    "storage",
    "activeTab"
  ],
  "background": {
    "persistent": false,
    "page": "background.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "src/content/injector.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "src/content/index.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "default_popup": "src/popup/popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "options_ui": {
    "page": "src/settings/settings.html",
    "open_in_tab": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "smarttabsound@addons.mozilla.org",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}