My computer is far from my router, so it disconnects frequently for short periods of time. When downloading files, if I notice that I have disconnected before Firefox does, I pause the download, and continue it when I reconnect. However, if I do not, it gives the message: "", and am forced to redo the download from the beginning. A similar issue was addressed in this ticket ([https://support.mozilla.org/questions/913829]). I will try this solution next time the error occurs, but I believe that firefox should integrate a retry mechanism (or at least, button) at this stage for the user to select once the internet connection has been re-established, to continue downloading from the point reached before disconnection (as pausing before firefox gives this error does not interrupt the download).