Examine source code of Envelop

{
  "name": "Envelop",
  "version": "1.0.2",
  "description": "Share private files easily",
  "manifest_version": 2,
  "background": {
    "scripts": [
      "browser-polyfill.min.js",
      "background.js"
    ]
  },
  "icons": {
    "128": "envelop-icon.png"
  },
  "browser_action": {
    "default_title": "Envelop",
    "default_icon": "envelop-icon.png"
  },
  "permissions": [
    "*://envelop.app/*"
  ],
  "commands": {
    "_execute_browser_action": {
      "description": "Open Envelop window",
      "suggested_key": {
        "chromeos": "Alt+Shift+E",
        "linux": "Alt+Shift+E",
        "mac": "Alt+Shift+E",
        "windows": "Alt+Shift+E"
      }
    }
  }
}