It's too easy install the latest Adobe Pepper Flash plugin for Firefox, Chromium or Vivaldi.
·Ubuntu/Linux Mint/Debian-64bit:
Open a Terminal 
and write these commands...
sudo apt-get update
sudo apt purge --remove adobe-flashplugin pepperflashplugin-nonfree flashplugin-installer
sudo apt-get install pepperflashplugin-nonfree
.......if this one doesn't work write this: sudo apt-get install adobe-flashplugin
sudo apt-get install browser-plugin-freshplayer-pepperflash
If you installed adobe-flashplugin(step 4b) write this: sudo rm -f /usr/lib/adobe-flashplugin/libflashplayer.so
Close and open your browser again.
September/2017...From Colombia, South America 