Download Flash Player 10 beta 2 for Linux from here. Save the .tar.gz file to your desktop.
Open your terminal, go to Desktop folder:
cd ~/Desktop
Unpackage the .tar.gz file:
tar zxvf flashplayer10_install_linux_070208.tar.gz
Go to install_flash_player_10_linux folder:
cd install_flash_player_10_linux
Installing Flash Player 10 beta 2:
cp libflashplayer.so ~/.mozilla/plugins/
That’s it. Restart Firefox.