Examine source code of focus-search

{
  "name": "focus-search",
  "description": "focuses the search input with alt+q (option+q on mac) on most websites",
  "manifest_version": 2,
  "version": "1.8",
  "homepage_url": "https://github.com/ieviev/firefox-focus-search",
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "main.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{68c3bf09-f9b0-4a1b-9080-d7c65be3c3be}"
    }
  }
}