Examine source code of YouTube Download Plus

{
  "manifest_version": 2,
  "name": "YouTube Download Plus",
  "version": "3.0.0",
  "default_locale": "en",
  "description": "Download buttons for YouTube videos.",
  "icons": {
    "64": "icon.png"
  },
  "applications": {
    "gecko": {
      "id": "addon@ytdownloader.info"
    }
  },
  "permissions": [
    "*://*/*",
    "activeTab",
    "notifications",
    "storage",
    "tabs",
    "webNavigation"
  ],
  "background": {
    "scripts": [
      "index.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "data/jquery-3.1.0.min.js",
        "data/modification-script.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": {
      "32": "data/youtube-download-active.png"
    },
    "default_title": "YouTube Download",
    "default_popup": "data/youtube-panel.html",
    "browser_style": true
  },
  "options_ui": {
    "page": "data/options.html"
  },
  "web_accessible_resources": [
    "data/download.png",
    "data/options.css"
  ]
}