From this comment: https://www.reddit.com/r/BitDefender/comments/1ovarkl/comment/noq97f5/ "Had this issue as well after Firefox updated today. I have found a solution but I am not sure if it just masks the problem or this was always the case. I noticed that the Firefox shortcut on the desktop changed into an executable so when I ran the app from the windows start menu which runs the "C:\Program Files\Mozilla Firefox\firefox.exe" by default, the cfg file does not appear on the desktop. It does appear in the firefox folder. I deleted the desktop executable and replaced it with the shortcut so it no longer causes the cfg file to appear on the desktop." Does this help?