Examine source code of 2ch font size changer

{
  "manifest_version": 2,
  "name": "2ch font size changer",
  "version": "1.0",
  "description": "Simple tool to set font size on 2ch.hk",
  "permissions": [
    "activeTab",
    "https://2ch.hk/*",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://2ch.hk/*"
      ],
      "js": [
        "content_script.js"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon-16.png",
      "48": "icons/icon-48.png",
      "128": "icons/icon-128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5dcc32d3-a781-4c4e-aadd-b1c955fe33e8}"
    }
  }
}