Нашёл 1 млн ответов for 'mozilla downlowder'.
https://addons.mozilla.org/en-US/firefox/addon/video-downloadhelper/
https://addons.mozilla.org/en-US/firefox/addon/video-downloader-profession/
https://www.downloadhelper.net/
https://www.downloadhelper.net/install
https://www.downloadhelper.net/install.php
https://www.mozilla.org/en-US/firefox/windows/
https://www.mozilla.org/en-US/firefox/new/
https://www.mozilla.org/en-US/firefox/all/
https://www.lifewire.com/downloading-tools-for-firefox-445586
https://www.guidingtech.com/10992/best-download-managers-for-firefox/