Examine source code of CaptureX

{
  "manifest_version": 2,
  "name": "Screenshot plugin",
  "version": "1.0",
  "description": "A plugin for taking screenshots",
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{31a6e887-8975-42f0-bf74-3205124ffff5}"
    }
  }
}