I have been using Firefox, for many years and Dishita's download program has been the best available on the net, when YouTube make changes he is on it straight away to get the down loader working again, he always responds to any emails, and he has created the fastest add free downloader that I can find, I highly recommend this Easy Youtube Video Downloader Express as the best out there.
Nine months later and I'm still using Dishita's fantastic program. I mainly use it to download youtube videos so I can watch them without the adds and then delete them. occasionally I save one for watching later. It's fast and makes watching Youtube videos a pleasure.