Debian: How to install Adobe Flash plugin for Firefox?

To be able to view most of flash player animations you should replace standard Shockwave Flash player with Adobe flash player (plugin) in your browser. In terminal switch to root and remove Gnash:

apt-get remove gnash

Now simply download tar.bz package with Adobe flash player from it's official site. Switch to destination where you've downloaded file and extract it:

cd /Downloads
tar xvf install_flash_player_11_linux.x86_64.tar.gz

Now copy extracted file of plugin into specific directory:

cp libflashplayer.so /usr/lib/mozilla/plugins/

Change working directory:

cd ./usr/bin/

Finally copy last thing:

cp flash-player-properties /usr/local/bin

Restart Firefox to apply changes.