What is a safe add-on to download youtube video and audio, something virus and malware free?

We do not really discuss add-on comparisons here, but note all officially hosted add-on extensions hosted on addons.mozilla.org and available from the Firefox User Interface will have been reviewed and be safe, secure and virus free. * Use Menu Button -> Add-ons -> [Search all Add-ons] <br />(Or key in to the Addressbar ''about:addons'') * Example [https://addons.mozilla.org/en-US/firefox/search/?q=video+download&sort=users&appver=34.0 search] (You may be able to do a better targeted search from your own machine) ** With >5M users top of the list is [https://addons.mozilla.org/en-US/firefox/addon/video-downloadhelper/ Video DownloadHelper] N.B. There may be possible legal &/or copyright issues with downloading some material, but that is out of scope of this support forum discussion.