Examine source code of Gmail++

{
  "manifest_version": 2,
  "name": "Gmail++",
  "version": "1.1.0",
  "description": "Improves the user experience of Gmail",
  "icons": {
    "48": "icons/icon-48.png",
    "64": "icons/icon-64.png"
  },
  "permissions": [
    "*://mail.google.com/",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/*"
      ],
      "js": [
        "lib.js",
        "main.js"
      ],
      "run_at": "document_end"
    }
  ],
  "options_ui": {
    "page": "options.html",
    "browser_style": true,
    "chrome_style": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "gmail-plus-plus@pfaff.dev"
    }
  }
}