Examine source code of Gmail Quick User Filter

{
  "manifest_version": 2,
  "name": "Better Gmail Helper",
  "version": "1.0",
  "description": "Extension for Gmail: in a conversation, click a subject profile image to view all conversations with that subject",
  "permissions": [
    "*://mail.google.com/*"
  ],
  "icons": {
    "128": "icons/icon-128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "js": [
        "dist/content.bundle.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{4dca1720-eceb-4d80-9a79-738fb0d9c10b}"
    }
  }
}