The following comment appears in dom/base/Document.cpp:

  // Calling StorageAllowedForDocument will notify the ContentBlockLog. This
  // loads TrackingDBService.jsm, which in turn pulls in osfile.jsm, making us
  // fail // browser/base/content/test/performance/browser_startup.js. To avoid
  // that, we short-circuit the check here by allowing storage access to system
  // and addon principles, avoiding the test-failure.

This is no longer the case and might consider re-evaluation.