ubun2

Yeah, it is annoying not having a apt-get url to install flash plugin for 64bit ubuntu.
 
Go to http://download.macromedia.com/pub/labs/flashplayer10/libflashplayer-10.... and download the tar.gz file and extract the contents i.e libflashplayer.so to your home directories .mozilla/plugins folder
 
for example copy it to the following folder (replace joe with your username)
 
/home/joe/.mozilla/plugins
 
NOTE: If there doesn't exist a plugins folder create one.
 
Close if any instance of browsers are opened. Now open firefox and enjoy your favourite flash sites.