Youtube - newbie guidance

[Richard Owlett <rowlett@cloud85.net>]

I use User agent: Mozilla/5.0 (X11; Linux i686; rv:51.0) Gecko/20100101 
Firefox/51.0 SeaMonkey/2.48 on a Debian Stretch machine with the MATE 
desktop.

I've never used youtube before.
I received a link to a youtube video 
<https://www.youtube.com/watch?v=82_bPWyrPFc> which played fine.

I did not have time to watch the whole video.
How can I download and save it?
   Its content is something I will wish to review and my data cap is
   low enough that I can not just repeatedly access it If I didn't get
   some point the creator was making.
Is there some way to pause a video if I'm interrupted?

I did some searches of Synaptic. There were some hopeful hits. Their 
homepages didn't tell me if they could do what I want.

I did some web searches but again came away confused.
I suspect I'm using wrong search terms &/or there is some underlying 
assumption that I'm missing.


TIA