Examine source code of CloseSpotifyTab

{
  "manifest_version": 2,
  "name": "CloseSpotifyTab",
  "version": "1.0",
  "description": "Closes a spotify tab after you've been redirected to the app.'",
  "icons": {
    "48": "icons/48.png",
    "96": "icons/96.png",
    "128": "icons/128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://open.spotify.com/*"
      ],
      "js": [
        "closeTab.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{8436891d-3fa8-4354-aed4-2b5953769062}"
    }
  }
}