On Windows systems, the logger run by the Windows updater...

Vulnerability Description

On Windows systems, the logger run by the Windows updater deletes the file "update.log" before it runs in order to write a new log of that name. The path to this file is supplied at the command line to the updater and could be used in concert with another local exploit to delete a different file named "update.log" instead of the one intended. Note: This attack only affects Windows operating systems. Other operating systems are not affected. This vulnerability affects Firefox < 55.

References

• https://www.mozilla.org/security/advisories/mfsa2017-18/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1234401
• http://www.securitytracker.com/id/1039124