As the name suggests, this is for speed. You click the extension icon while watching a video, and the download starts in the background. It uses Firefox’s built-in download manager, so you don't need third-party software. It is open-source and contains no adware.
This is the only solution that has worked consistently for five years and will likely work for five more.
This is an important topic to address. While the tools are free, downloading copyrighted music from YouTube without permission is against YouTube's Terms of Service. Many content creators rely on ad revenue and views, and downloading their work can impact that. Additionally, legal actions have been taken against some of the most popular "stream-ripping" services, highlighting the risks involved.