The download helper use to be very good, but now it no longer provides the same service. Previously it provided multiple options for downloading a video but now only provides one from ADT. ADT is extremely slow in downloading and often the download fails to complete. On occasion it downloads the video but not the audio. I use it both on Win 10 and Linux Open Suse.

The problems I am guessing occurred via some updates, not sure if it was Firefox or Download Helper. I did not make any changes so it had to be a change in the software. I wish there were a better plugin since this one no longer provides proper service.