download from Softpedia the 64-bit flash player.
sure to close Firefox before proceeding.
uninstall the 32-bit version before installing the 64. Go to "System -> Administration -> Synaptic Package Manager" and try nsplugin . Click on the green box in front of nspluginwrapper and select "Mark for complete removal." There also will be asked to remove the "flashplugin-nonfree" remove that too.
Extract the file you downloaded, go to the directory / home / username / .mozilla (it's a hidden folder, to see it go to "View-> Show Hidden Files"), created within. Mozilla new folder with the name of plugins. Copy the extracted file into the new folder.
You have now installed the 64 bit flash player.
