Examine source code of Grid Overlay

{
  "manifest_version": 2,
  "name": "Grid Overlay",
  "version": "1.0",
  "description": "Overlay a customizable grid on any webpage to help with design alignment.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{564117f4-40b9-4df6-b5d9-8009c26fb36d}"
    }
  }
}