When Private Browsing mode is used, it is possible for a web worker to write persistent data to IndexedDB and fingerprint a user uniquely. IndexedDB should not be available in Private Browsing mode and this stored data will persist across multiple private browsing mode sessions because it is not cleared when exiting.
Name: the Mozilla project
This issue has been addressed in the following products:
Red Hat Enterprise Linux 6
Red Hat Enterprise Linux 7
Via RHSA-2017:3382 https://access.redhat.com/errata/RHSA-2017:3382