Could you please send a few links you can't download. We will check it out.

Hello, in the Firefox browser you have an extension of the current version.

First, reinstall the extension from this link: http://download.sf-helper.com/mozilla/helper_last.html

Before downloading, make sure that the music you want to download is not by subscription, since we cannot download it.

Hello. For subscription related issues, refunds and problems with activation, please, write at: help@ummy.net

Hello, to download a video with sound, use the program Televzr: https://desktop.televzr.com

We don’t have the ability to download videos with sound, extension or via the website.

Hello! Due to the recent youtube changes, both our website and the add-on are enable to download in 720p.
We are trying to bypass it, but with no luck yet. For now, we can recommend switching to Televzr app, that can download in 720p and higher:
https://desktop.televzr.com/#

Hello, unfortunately we do not have this opportunity.

Hello, it's not our fault that youtube decided to get rid of 3gp . There is nothing we can do about it.