There is a newer version of that extension available here: https://addons.mozilla.org/en-US/firefox/addon/download-youtube/versions/

Thank you - most recent version is 1.8.5 dated 12/19/15 however Firefox cautions usage as Mozilla has not yet reviewed - do you recommend installing anyway? Obviously I've had little experience with add-ons.

Note that that is a different extension than the one you have installed.

• Video DownloadHelper (VDH): https://addons.mozilla.org/firefox/addon/video-downloadhelper/

Another extension you can look at if you do not need to convert files:

• Youtube Video and Audio Downloader: https://addons.mozilla.org/firefox/addon/youtube-video-and-audio-dow/