This is one of the more robust options because it leverages yt-dlp , a powerful command-line tool, while keeping a simple browser interface. : Explicitly supports downloading complete YouTube playlists .
I use Video DownloadHelper as an addon for Firefox which is allowing me to download them and they play fine. Video DownloadHelper Video Downloader youtube playlist downloader firefox plugin
This extension is specifically designed for batch downloading. Instead of just a single "Download" button, it adds options for entire playlists and channels. This is one of the more robust options