Edited Oct 5,'21 because as a result of the 'IdentTrust' problem, see viewtopic.php?p=38360#p38360, even more websites will no longer permit access via seamonkey2.46.
AFAIK, all current firefox, chromium & clones enable the installation of addons/extensions. Among those are such video download apps as video downloadhelper. Using these you can download a video rather than just steam it.
What isn't obvious is that rather than Left-Click the Download/Save button or equivalent, several will display a "copy url" to clip-board or equivalent option if you Right-Click that button.
Having copied the source URL to the clip-board, you can then Menu>Internet>uGet and paste that URL into its source field. [Opening uGet may have done this automatically]. With uGet downloading the source-file, your web-browser is now free to use for other activities: it no longer has to remain on the source-files web-page.
Which addon/extension your browser can use, which can be used with various web-sites, and which offers a Right-Click option can only be determined by trial-and-error.
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The following may still work in some cases:
I don't think it matters what the content is. AFAIK, the easiest way to record any streaming media --while it still functions is--
Seamonkey portable 2.46 with
ca-archive installed from here, https://github.com/JustOff/ca-archive
which is then used to install netvideohunter 1.20.
Netvideohunter can directly download videos. But with a little exploring of the download drop-down mechanism, the url of the stream itself can be copied to the clip-board and from there passed to uget.
Seamonkey 2.46 is the last under which Netvideohunter will function. [Of course, you don't need the portable; but then you'd have to resolve dependencies on your own*].
Seamonkey 2.46 is now 5 years old. Increasingly websites refuse to allow access, demanding newer web-browsers. Palemoon and Waterfox-classic can both use the ca-archive+netvideohunter combo but netvideohunter, itself, can't handle some recent codec/containers? and so doesn't see some streams.
There are up-to-date 'video-download' addons/extensions for more recent web-browsers. Probably worth exploring when netvideohunter ceases to be reasonably functional.
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* See post here. viewtopic.php?p=8330#p8330. It also works with Seamonkey.