Video Downloadhelper works fine on one account and bad on the other. Why?

[HitTheRoad]

I'm on a Mac, using Video Downloadhelper for Firefox.
The strange thing is: on my one account on this Mac Video Downloadhelper works fine, offering me playable mp4 and flv downloads, and on the other account it seems Video Downloadhelper unnecessarily tries to convert all downloads and then gives me QR watermarked downloads or unplayable downloads.

On both accounts I use the same, most recent version of Video Downloadhelper and Firefox.

It doesn't matter what website I download from. Everywhere I get the same outcome: Video Downloadhelper working fine on my one account, and bad on the other.

I thought maybe on the account, where Video Downloader doesn't work, other addons obstructed Video Downloadhelper. I turned them all off, but that didn't help.

Anyone any idea how this can be explained and solved?

[Krispy Kritter]

and on the other account it seems Video Downloadhelper unnecessarily tries to convert all downloads and then gives me QR watermarked downloads or unplayable downloads.

Sounds like the configuration on this account is set to convert the downloads.

Compare the configuration between the two accounts.

[HitTheRoad]

Settings are the same.

[Krispy Kritter]

Actually, looks like the converter portion of that app is a separate addon> https://www.downloadhelper.net/conversion-manual

In any case, something is running which is capturing the download and attempting to convert (and which is also apparently adding the watermark). As you are on a Mac and not Windows, I don't know the process to see which applications are running. But I'd start with anything similar to "QR".

[HitTheRoad]

Sorry. I was mistaken! One the account, where Video DownloadHelper, isn't working, as conversion program was installed: avconv.
I'm trying to find a way to uninstall the program, but until now without success. It looks like it isn't possible to do this from the settings of Video Downloader.