deb http://ftp.ca.debian.org/debian/ stretch main contrib non-free
deb-src http://ftp.ca.debian.org/debian/ stretch main contrib non-free

deb http://security.debian.org/debian-security stretch/updates main contrib non-free
deb-src http://security.debian.org/debian-security stretch/updates main contrib non-free

# stretch-updates, previously known as 'volatile'
deb http://ftp.ca.debian.org/debian/ stretch-updates main contrib non-free
deb-src http://ftp.ca.debian.org/debian/ stretch-updates main contrib non-free

deb http://download.virtualbox.org/virtualbox/debian stretch contrib
deb http://www.deb-multimedia.org stretch main non-free
deb [arch=i386,amd64] http://mariadb.mirror.globo.tech/repo/10.2/debian stretch main

sudo apt-get install flashplugin-nonfree
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package flashplugin-nonfree is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or is only available from another source

E: Package 'flashplugin-nonfree' has no installation candidate

chmod 644 /usr/lib/flashplugin-nonfree/libflashplayer.so
chown root:root /usr/lib/flashplugin-nonfree/libflashplayer.so

update-alternatives --list flash-mozilla.so

update-alternatives --quiet --install /usr/lib/mozilla/plugins/flash-mozilla.so flash-mozilla.so /usr/lib/flashplugin-nonfree/libflashplayer.so 50