Flash

64-bit on Linux
Download the latest 64-bit plugin

$ sudo apt-get purge flashplugin-nonfree gnash gnash-common mozilla-plugin-gnash nspluginwrapper swfdec-mozilla

$ tar xvzf libflashplayer-*.linux-x86_64.so.tar.gz

Replace the $PATH below with ~/.mozilla/plugins for only yourself as a user, the steps below install it system wide.

$ sudo mv libflashplayer.so /usr/lib/mozilla/plugins/libflashplayer.so

Restart Firefox and type

about:plugins

in the URL bar to make sure it's installed.