Examine source code of CSSer

{
  "manifest_version": 2,
  "name": "CSSer",
  "version": "1.15",
  "description": "Set Custom CSS for Code on All Web pages you Visit.",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "pretty.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "pretty@sendokame.netlify.app"
    }
  }
}