I think the first reviewer didn't give this a fair trial - it's wonderful!

Yes, you need to download the extra piece of software to your computer (but so do several other video downloaders). This one sits on your desktop, and works beautifully with Firefox 57 and Windows 10 (latest version).

As I have downloaded 6 other video downloaders in the past 2 days (and unistalled them because they simply didn't work) I am so happy to have found one that does the job. I highly recommend this one.