Examine source code of GoogEvening - Alpha ver.

{
  "manifest_version": 2,
  "name": "GoogEvening",
  "version": "1.1.2resigned1",
  "description": "Adds a dark background to google search site",
  "icons": {
    "48": "icons/moon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.google.com/search*",
        "*://www.google.com/"
      ],
      "js": [
        "GoogEvening.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{58171287-4470-4a69-aa72-445150bafd8f}"
    }
  }
}