Examine source code of Session Restore Helper

{
  "manifest_version": 2,
  "name": "Session Restore Helper",
  "version": "1.0",
  "description": "Ensures previous session tabs are restored at every Firefox start.",
  "permissions": [
    "sessions",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "session-restore-helper@example.com"
    }
  }
}