the best for youtube

For 1080p and higher, it can download only video without sound, and separately the audio.

According to:
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https://support.mozilla.org/en-US/kb/permission-request-messages-firefox-extensions#w_access-your-data-for-all-websites

The extension can read the content of any web page you visit as well as data you enter into those web pages, such as usernames and passwords.
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According to:

https://securitywithsam.com/2019/07/dataspii-leak-via-browser-extensions/

this is spyware.