I have tried to follow the steps recommended in https://linuxconfig.org/enable-adobe-flash-for-firefox-on-ubuntu-20-04-focal-fossa-linux
But when I enter sudo apt install flashplugin-installer into my shell, it tells me the package flushplugin-installer could not be found.
REMARK: I know flash is an old software virtually no one uses anymore, but I need it in order to view content embedded in newspaper articles that were published ten years ago.