Examine source code of Bookmark2Toolbar - Twitch

{
  "description": "Add a Twitch bookmark to the toolbar",
  "manifest_version": 2,
  "name": "Bookmark2Toolbar - Twitch",
  "version": "1.0.0",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/ico16.png",
      "32": "icons/ico32.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "86darv@gmail.com.twitch"
    }
  }
}