Until the 6 of September 2020 it was a good add-on, then this ugly QR-Code started to appear. I thought about paying for this service, but paying is too intransperent so I couldn't. Recently it also started to download mp4 whithout audio, and the mkv are always damaged and have noise instead of audio, when displayed as download-Option.
Whithout beeing able to download with audio I don't feel like paying for this at all.
Also https://www.downloadhelper.net/asites/f/standard/1 still advertises with youtube beeing downloadable while this is not the case anymore.
For years this was one of the best add-ons for firefor but now live recorder is better, as long as you are able to convert webm back to mp4.