Examine source code of TabbyBARA

{
  "manifest_version": 2,
  "name": "TabbyBARA",
  "version": "1.0",
  "description": "Adds a shortcut (Ctrl+Shift+E) to open a new tab in the same tab group as the current tab - right after the currently active tab.",
  "permissions": [
    "tabs",
    "cookies",
    "contextualIdentities",
    "tabGroups"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "commands": {
    "open-container-tab": {
      "suggested_key": {
        "default": "Ctrl+Shift+E",
        "mac": "Command+Shift+E"
      },
      "description": "Open a new tab in current tab group - right after the currently active tab"
    }
  },
  "icons": {
    "16": "icons/icon-16.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d8e88af6-23d0-4b7d-aedd-252b3d8ba79a}"
    }
  }
}