Examine source code of UPPERCASE

{
  "manifest_version": 2,
  "name": "UPPERCASE",
  "version": "1.0",
  "author": "katchov",
  "icons": {
    "64": "uppercase.svg"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "uppercase@katchov"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "css": [
        "uppercase.css"
      ],
      "all_frames": true,
      "run_at": "document_start"
    }
  ]
}