Examine source code of Custom Page Layouts

{
  "manifest_version": 2,
  "name": "Custom Page Layouts",
  "version": "1.0",
  "description": "Choose grid or column layouts for articles.",
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Custom Page Layouts"
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{57ef57a0-a0d0-4a0c-820a-4c80560c5d54}"
    }
  }
}