Examine source code of Custom Theme Changer

{
  "manifest_version": 2,
  "name": "Custom Theme Changer",
  "version": "1.0",
  "description": "Change the browser toolbar's background color.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "permissions": [
    "theme"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{c7ec49e1-968f-4fe6-90a3-bff6179631c4}"
    }
  }
}