Did not work. Running Firefox 60.4.0esr (64-bit). Attempted twice to download a 90 minute video from YouTube. According to NetWorx, VDH downloaded all 1700 megabytes of the MP4, but after the download was completed, all that was in the download folder was a 100 mB clip with only a few seconds of the beginning of the video. And it was not in the folder that I had specified in Settings. A search of the hard drive failed to uncover just where the app had placed the 1700 mB data stream while it was downloading, so I assume the app erased it. Removed this extension, I'll have to try and find something else.