Examine source code of Page Audio Booster

{
  "manifest_version": 2,
  "name": "Page Audio Booster",
  "description": "Boost the volume of all audio/video elements on the page with adjustable gain",
  "version": "1.0",
  "icons": {
    "64": "icons/icon-64.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icons/icon-64.png",
    "default_title": "Page Audio Booster",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{2539b20a-8b9e-4b01-b58c-7a306152f3e8}",
      "strict_min_version": "90.0"
    }
  }
}