sudo wget https://fpdownload.macromedia.com/pub/labs/flashruntimes/flashplayer/linux64/libflashplayer.so -O /usr/lib/adobe-flashplugin/libflashplayer.so
#or
cd /usr/lib/adobe-flashplugin
sudo wget -N https://fpdownload.macromedia.com/pub/labs/flashruntimes/flashplayer/linux64/libflashplayer.so
#or
sudo curl https://fpdownload.macromedia.com/pub/labs/flashruntimes/flashplayer/linux64/libflashplayer.so > /usr/lib/adobe-flashplugin/libflashplayer.so
#check
firefox http://www.adobe.com/swf/software/flash/about/flashAbout_info_small.swf