Examine source code of UA Changer

{
  "manifest_version": 2,
  "name": "UA Changer",
  "version": "1.0",
  "description": "Quickly and easily switch between popular user-agent strings.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a8e37745-b940-4b29-9078-d8c51b6e67e0}"
    }
  }
}