Examine source code of Rainbow Headers

{
  "manifest_version": 2,
  "name": "Rainbow Headers",
  "version": "1.0",
  "description": "Change the color of article headers to a rainbow gradient.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{664f9b55-8abc-4692-9c1d-3b38ec463128}"
    }
  }
}