via the Firefox Add-ons manager. If the extension appears active but fails to download, it often indicates a need for a "Companion App" (like the one for Video DownloadHelper ) to handle high-resolution files and playlist merges. Step-by-Step Fixes for Firefox Downloader Plugins Force an Extension Update Open the Firefox menu and select Add-ons and themes above your extensions and select Check for Updates Install Necessary Companion Apps Many plugins like Video DownloadHelper
Ensure the extension has permission to access youtube.com and googlevideo.com . Go to about:addons → extension → Permissions → enable “Access your data for all websites” if needed. youtube playlist downloader firefox plugin fix