Examine source code of TabNav

{
  "manifest_version": 2,
  "name": "TabNav",
  "version": "1.3resigned1",
  "description": "Navigate between tabs using arrows.",
  "icons": {
    "24": "icons/icon24.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "background": {
    "scripts": [
      "main.js"
    ]
  },
  "applications": {
    "gecko": {
      "id": "thomas.introini@gmail.com",
      "strict_min_version": "60.0"
    }
  },
  "commands": {
    "previous-tab": {
      "suggested_key": {
        "default": "Alt+Shift+Left"
      },
      "description": "Change to previous tab"
    },
    "next-tab": {
      "suggested_key": {
        "default": "Alt+Shift+Right"
      },
      "description": "Change to next tab"
    }
  }
}