Promts me to install another program in order to proceed downloading a video. I reported this to mozilla.

useless crap, don't waste your time.

Adiciona un WaterMark y además solicita la instalación de un plug-in adicional

kræver ekstra program installation.

You have to install a separate installer. They put a watermark and you must pay it to remove the watermark.

Watermark

It's a converter, not a downloader. As such, it's much slower and resource intensive than it needs to be. It also watermarks the video.

1. This extension is proprietary non-free software. The license is proprietary and only allow you to use the software, with all other rights reserved (see "License" under "More information"). The source code of this extension is _NOT_ available
2. It requires an external application to be installed on your system in order to run

下载youtube试了好多次，每次都是卡在汇总中。不好使！

Doesn't allow downloading without also installing a dangerous external EXE.

Why do I need a companion app?

This requires a "companion app" that looks shady

Bad video compression and worst of all: A big-ass QR-code in the corner of the screen unless you pay up. Could have been upfront about it, I would not have wasted my time.

Including a Watermark it's just nasty.