The 32bit flash player works just fine on my 64bit firefox. All you need to do is install the flashplayer files and enable them via nspluginwrapper.
The only hurdle is that the installer program distributed by Adobe doesn't work on 64. You have to download the tar.gz version from here
, untar it, and copy the two files (libflashplayer.so and flashplayer.xpt) by hand to a location such as /usr/lib/browser-plugins/.
Then, all you need to do is direct nspluginwrapper to the plugin with the following command:
nspluginwrapper -i /usr/lib/browser-plugins/libflashplayer.so
That's it. The plugin should be working in your x86_64 Firefox and Mozilla. about
:plugins should confirm it.
See the Mozilla plug-in FAQ
for more info on 64bit support.