In particular it is possible to download again all the videos to have a local copy to watch when we are not able to use the internet.
The team of DdownloadHelper was professional and fast to solve this annoying problem which was caused by changes operated by YouTube on its website. For all the people who has not already used this add-on before, I remind you that DownloadHelper is, in my opinion, the most advanced tool to navigate YouTube videos, download contents for evaluation and directly convert the format from flv to mp4 or other video format you prefer.
For the record, this problem caused the same malfunctioning to all the software with similar features. In particular, you could have problems when using Gmediafinder for Linux (at least we have had this kind of matter during the past weekend).