Examine source code of Let Me Focus

{
  "manifest_version": 2,
  "name": "Let Me Focus",
  "version": "1.0",
  "description": "Removes the Twitter sidebar",
  "homepage_url": "https://liberapay.com/andrewwhocodes",
  "icons": {
    "48": "icons/icon_128.png"
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.twitter.com/*",
        "*://twitter.com/*"
      ],
      "js": [
        "main.js"
      ]
    }
  ]
}