Examine source code of Better Volume

{
  "manifest_version": 2,
  "name": "Better Volume",
  "version": "2",
  "description": "Allows you to set domain volume from 0-600% with 1% increments between 0% and 10%. Volumes are saved between sessions, as well as per domain.",
  "icons": {
    "24": "icons/icon_24.png",
    "32": "icons/icon_32.png",
    "48": "icons/icon_48.png",
    "64": "icons/icon_64.png",
    "128": "icons/icon_128.png",
    "256": "icons/icon_256.png",
    "512": "icons/icon_512.png"
  },
  "background": {
    "persistent": true,
    "scripts": [
      "js/background.js"
    ]
  },
  "content_scripts": [
    {
      "all_frames": true,
      "js": [
        "js/contentscript.js"
      ],
      "matches": [
        "http://*/*",
        "https://*/*",
        "file:///*"
      ],
      "run_at": "document_start",
      "match_about_blank": true
    }
  ],
  "permissions": [
    "<all_urls>",
    "tabs",
    "activeTab",
    "storage"
  ],
  "browser_action": {
    "default_icon": {
      "24": "icons/icon_24.png",
      "32": "icons/icon_32.png",
      "48": "icons/icon_48.png",
      "64": "icons/icon_64.png",
      "128": "icons/icon_128.png",
      "256": "icons/icon_256.png",
      "512": "icons/icon_512.png"
    },
    "default_title": "Better Volume",
    "default_popup": "popup/popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{f9958fd6-dfc7-45d7-965c-8a87ed886ef2}"
    }
  }
}