64-bit Firefox and 64-bit Flash plugin

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1. Remove currently installed versions of Flash.

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

1. Visit http://labs.adobe.com/downloads/flashplayer10.html to update the filename given under if necessary.
2. Download the 64-bit Flash plugin and extract it:

wget http://download.macromedia.com/pub/labs/flashplayer10/libflashplayer- && tar xvfz libflashplayer-

1. Move the file in /usr/lib/mozilla/plugins for a site-wide install (or in ~/.mozilla/plugins for a single-user install):

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