- Download 64 bit plugin from this direct link (I'm not sure how long this URL will be available).
- Uncompress the downloaded file and copy(as root user) the shared object(libflashplayer.so) to /usr/lib64/mozilla/plugins/.
Restart Mozilla Firefox and visit about:plugins to verify the plugin. The above steps have been tested in Firefox-3.6.4 running on Fedora 13.
Caveat: Adobe flash-plugin is not FOSS.