Firefox may kill the playlist parser if it takes >5 seconds.
If you want, I can:
Since you referenced an article with that specific title, you are likely dealing with the common frustration that browser extensions (like Firefox plugins) are terrible at downloading YouTube playlists. youtube playlist downloader firefox plugin fix
If you are looking for the "fix" mentioned in that type of article, here is the summary of the situation and the actual working solutions. Firefox may kill the playlist parser if it
A: Do not do this unless you trust the developer absolutely. Download the .xpi file from the developer’s GitHub, then drag it into about:addons. You will bypass Mozilla’s security review. If you want, I can:
A: Only if the plugin supports cookie export (security risk). Never paste your cookies into an untrusted plugin. Instead, use a local tool like yt-dlp --cookies-from-browser firefox.