Sur debian amd64

apt-get install nspluginwrapper
wget http://fpdownload.macromedia.com/get/flashplayer/\
current/install_flash_player_9_linux.tar.gz
tar xzvf install_flash_player_9_linux.tar.gz
mv install_flash_player_9_linux/flashplayer.xpt \
    install_flash_player_9_linux/libflashplayer.so \
    ~/.mozilla/plugins/
nspluginwrapper -i ~/.mozilla/plugins/libflashplayer.so