I only use Firefox for downloading web videos so I'm still on 56. Which was fine for a while. I just kept it from updating But somehow Mozilla fucked extensions up a few weeks ago even on older unupdated browsers so TabMixPlus doesn't work anymore. So I might as well just update to whatever the new Firefox version is. I just need DownloadHelper and I think it works there now. But I'd rather it have stayed how I had it with TMP still working. I need my multiple tab rows in Firefox. I can't believe Mozilla was able to fuck up extension support without even updating the browser. WTF?
Safari is just so much nicer on macOS ever since Apple started caring about it a while ago.
Check out the command-line app "youtube-dl". It'll probably do what you want, and with little overhead.