Hello afalanga,

You should download Adobe Flash from here (and choose your own system) :

https://get.adobe.com/flashplayer/otherversions/

It will show in Firefox => Add-ons => Plugins as "Shockwave Flash".

afalanga said

I've read the articles and know that NPAPI plugins aren't supported now. However, this article, https://support.mozilla.org/en-US/kb/npapi-plugins, states that Adobe Flash should still work. I have installed the RPM, I've unpacked tarballs, placed libflashplayer.so in /usr/lib64/firefox/browser/plugins and just about everywhere else that various hits have instructed and still it doesn't work. So, what's the magic?

Try creating a folder as plugins in /home/username/.mozilla/ and then place the libflashplayer.so you extracted from the tarball in that newly created plugins folder.

Flash will not update this way as it is manually done.

Also if Firefox was still running when you do this, either restart Firefox or in type about:plugins in the Location (address) bar. This will make Firefox scan for the Flash Player Plugin.