Examine source code of Gmail Reply All Reminder

{
  "manifest_version": 2,
  "name": "Gmail Reply All Reminder",
  "version": "1.0.2",
  "description": "Adds a banner to remind to reply all when there are multiple email recipients.",
  "icons": {
    "48": "icons/replyall-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/mail/*"
      ],
      "js": [
        "replyAllRem.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{15828a3b-aeaf-4f47-a994-3ac52c4d4a73}"
    }
  }
}