The file picker dialog can choose and display the wrong local default directory when instantiated. On some operating systems, this can lead to information disclosure, such as the operating system or the local account name. This vulnerability affects Firefox < 52 and Thunderbird < 52.
https://www.mozilla.org/security/advisories/mfsa2017-09/
https://www.mozilla.org/security/advisories/mfsa2017-05/
https://bugzilla.mozilla.org/show_bug.cgi?id=1319370