Examine source code of Append string after URL

{
  "manifest_version": 2,
  "name": "Append string after URL",
  "description": "For my personal use: Add '/videos' to 'youtube.com' urls when clicking using 'Ctrl + Alt + Left Click'",
  "version": "5.0",
  "author": "justdecodeme",
  "icons": {
    "64": "icons/icon-64.png"
  },
  "background": {
    "scripts": [
      "background_script.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": {
      "64": "icons/icon-64.png"
    },
    "default_popup": "browserAction/index.html",
    "default_title": "Append string after URL"
  },
  "permissions": [
    "<all_urls>",
    "tabs",
    "activeTab",
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e80d16d5-bc93-4caa-8d85-2f463ab63603}"
    }
  }
}