Examine source code of Twitch Chat Width

{
  "manifest_version": 2,
  "name": "Twitch Chat Width",
  "version": "1.0",
  "description": "Change Twitch chat width in theatre mode.",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "icons": {
    "48": "tw.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.twitch.tv/*"
      ],
      "js": [
        "main.js"
      ]
    }
  ],
  "browser_action": {
    "default_title": "Click to set Twitch chat width size in theatre mode.",
    "default_popup": "size_input.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "go.hacker800@passinbox.com"
    }
  }
}