A Watermark stick on the video, there is plenty of software do better than this

Watermark switch and bait. Not working as advertised. Holding downloaded video hostage after losing 3 hours uselessly "sum" downloaded video - probalby spending it only for adding watermark.

It adds a watermark and asks for 30$ to remove it!

Ужасное "дополнение", ничего не понятно. Функций нагородили немеряно, а толку нет.

Completely useless. Keeps trying to install some additional app on my computer (probably a virus) and even when installed it still doesn't work.

watermarks=trash

The free version is worthless. I tried to download The Phantom of the Opera yesterday. it tool about 14 hours and the result was more than 2 hours of a blue screen with a QR code.

Used to be great: it would just mux the raw content together with ffmpeg in companion app. Now it wants to spend days slowly re-converting video just to add a QR-code watermark!? This change alone took it from a 5-star to a 1-star add-on.

"Companion app required".

VDH has been great up until the 7.3.9 release. It then started behaving bad, as in starting, but never completing video downloads in linux. I tracked this stopping to a build with a library(GLIBC) version that is ahead of many linux distributions. Researching in Google, VDH personnel are claiming that it is not their problem and are doing nothing. GLIBCs normally work if the program build is on a lower version than the distribution. It seems like VDH only needs to build using an earlier GLIBC version.
4/17/20 update -- I checked a windows version and I get the same strange behavior of hanging in the middle of a download forever. Manually stopping it in windows, unlike linux, does not result in any error message.
5/9/20 Loaded up Coapp 1.5 and tested again. Did not work any better. Still getting the same errors(below) and only ".parts" of warying sizes.
Errors:
Exit code: 1
/usr/local/net.downloadhelper.coapp-1.5.0/converter/build/linux/64/ffprobe: /lib64/libm.so.6: version `GLIBC_2.27' not found (required by /usr/local/net.downloadhelper.coapp-1.5.0/converter/build/linux/64/libavfilter.so.7)
/usr/local/net.downloadhelper.coapp-1.5.0/converter/build/linux/64/ffprobe: /lib64/libc.so.6: version `GLIBC_2.27' not found (required by /usr/local/net.downloadhelper.coapp-1.5.0/converter/build/linux/64/libavformat.so.58)
/usr/local/net.downloadhelper.coapp-1.5.0/converter/build/linux/64/ffprobe: /lib64/libm.so.6: version `GLIBC_2.27' not found (required by /usr/local/net.downloadhelper.coapp-1.5.0/converter/build/linux/64/libavcodec.so.58)

Changed from a useful app to a cash grab. Uninstalling.

Después de horas descargando un video para quitarle el ruido y poder oir bien la conferencia resulta que te pone una marca de agua y ahora lo que no puedo hacer es verlo bien. Vaya perdida de tiempo...
Además es incomodo de usar.

flashgot was my all time favorite download addon, but firefox new architecture killed it (for sure to much efforts to implement. i still was happy, cause this time was spend to noscript, an other project from the creator of flashgot).
then this video downloadhelper addon was heavily promoted on firefox addon website, even if it was just a dim light compared with its bright predecessor. i installed it cause for lack of alternatives and most of the time, it did its job, even if it had sometimes issues and wasnt as compfy as flashgot.
and now it demands money (30$/20€) to remove a watermark, that itself has encoded in the downloaded video.
the new art of blackmailing! time to move on..

1.) This is not a complete app—it requires another "companion app" in order to function. This other app is not available through the Firefox extensions page and requests more access permissions. If I were a computer programmer/app developer, I could perhaps review for myself the source code for specific evidence of nefariousness, but I am not.

2.) I would have given 2 stars, but the .mp4s I was able to download were corrupted. Downloading and converting at the same time requires the companion app, and another, third app, as well. I will not be downloading two further apps from a website I don't know just because of the presence of this half-functional app on the Firefox extensions page.

Hence, 1 star, and uninstalling.

AVOID!!! Do not waste your time on this add-on.
Downloaded a video, took 9 hours after converting to "aggregate," and after all that - they had the NERVE to add a big ugly QR code on the video, and tell you you need to purchase the premium version.
At least they could have warned you before downloading (or better yet, just disable it altogether so people don't waste their time).
Find an alternative - there are plenty out there that will be more upfront and work better.
Pity I can't give it zero stars, but at least it does work for some videos, so maybe it still earns this one star.

Used to great, now it's just "gimme muni lol".