"Easy Youtube Video Downloader Express" (by Dishita) is one of the extensions always installed in Firefox on any of the PCs I use to access the Internet. The extension has worked flawlessly for me since I began using it.

RATING/REVIEW UPDATE (as of 2024-11-10): "Easy Youtube Video Downloader Express" has not been functioning consistently since the last update in May 2024. (I am "Pro Upgrade" user.) Up to that point in time this extension functioned flawlessly. Updates were released fairly quickly whenever YouTube changed/tightened their policies on video downloads and ad-blocking. This is the reason for the change in rating from "5 stars" to 1.