A: No. Because YouTube is a moving target, no plugin offers 100% reliability. The best current record belongs to (command-line), which fixes breaks within 24 hours. For a GUI in Firefox, Video DownloadHelper has the fastest update cycle (2-5 days).
Ensure both your Firefox browser and the extension are running the latest versions. youtube playlist downloader firefox plugin fix
If you want a GUI (buttons and windows) and are coming from a Firefox plugin, is the answer. is the answer.