Firefox 72.0b3 (32-bit) Ever since (I believe) Firefox 71 or 72, downloads with an application associated have been failing with this message in the Downloads window: C:\Users\User\Downloads\Ant Videos\white_smith.zip could not be opened, because an unknown error occurred. Try saving to disk first and then opening the file. This happens whenever I download OR try to open files that will be automatically opened by helper application e.g. Windows Explorer, Winrar.