There are other ways; and maybe the use of the netvidohunter addon has been mentioned before. But I can't find a specific thread.
The easiest way to download almost all videos from anywhere, including Youtube, maybe to install the netvideohunter addon into any firefox, seamonkey or palemoon. Unfortunately, it's an xpi file which is no longer supported by current 'mozilla' and clones. No matter. Just install the "ca-archive-2.0.1.xpi" from here, https://github.com/JustOff/ca-archive/releases* --thanks, 666philb. After installation an orange icon will appear on your toolbar. Right-Click it and it you'll be taken to a search page of all the "75,929 versions of 16,706 Firefox add-ons created by 12,538 developers over the past 15 years". After that, it's almost a simple install. Almost because your system may not be fully functional with the first version the addon finds.
In 32-bit Seamonkey 2.46, I had used the 1.9.5fx.xpi of netvideohunter and had downloaded and stored it for use in other browsers. That version of Seamonkey still accepted xpi addons; but the last build of netvideohunter, version 1.20, hadn't worked.
In Palemoon64-28.7.0 with the ca-archive-2.0.1.xpi installed, 1.9.5fx.xpi installed, selecting a file for download seemed to work, but nothing in fact downloaded. So I uninstalled the 1.9.5fx.xpi version and installed the 1.20 version. Downloading a Youtube or other video once again became a simple matter of figuring out which of the several downloadable files netvideohunter finds is the one you want.
Hint, removing all files netvideohunter lists before pressing play helps. ca-archive-2.0.1.xpi locates the latest version of an addon. To find older versions look for and click the link saying "View all XX versions".
* You'll also find there a ca-archive-2.0.2b1.xpi untested by me. I assume it's newer and the 'b1' signifies "beta 1".