So I’ve gone back to Linux from Mac, due to the SSD issues I had with my Macbook Pro basically making VMware unusable. A Win7 VM would grind the guest and host to a halt on the 7200 RPM SATA OEM drive, and the SSD wouldn’t work, so I put the SSD back in my HP and installed CentOS 6 x86_64. Not really ideal, but at least it works.
CentOS 6 ships with Firefox 3.6.9, which is really old by now. Fine for a server, but I wanted FF6. I grabbed the Firefox 6.0.1 bz2 from VoxCast, unzipped it and copied it to /usr/lib64/firefox-6. Then I ran yum remove firefox to remove 3.6.9 and avoid any issues. I tried the instructions from my older post on this subject but for whatever reason it didn’t work – I’m guessing because I’m not using the distro’s Firefox RPM.
I followed these instructions to get the Flash 11 64-bit plugin installed. It still wasn’t working though.
I ended up creating a symlink:
ln -s /usr/lib64/mozilla/plugins/libflashplayer.so /home/evan/.mozilla/plugins/libflashplayer.so
When I started up Firefox after creating the symlink, Flash worked.
Additionally, to set Firefox 6 as the default browser, run gnome-default-applications-properties, select Custom, and paste /usr/lib64/firefox-6/firefox %s in the Command: field.
Update: I upgraded my home desktop PC from FC12 to FC14 last night and used the above procedure to install Firefox 6.0.2 on it with Flash 11. So, in case anyone was wondering, the above works for Fedora as well.
Evan Hoffman's Blog 
Thanks for you post. In fiddling around with the Flash plugin it seems Firefox is looking in /usr/lib/mozilla/plugins instead of /usr/lib64/mozilla/plugins. While it may not be the safest solution, you can get Flash to work globally by making this link:
ln -s /usr/lib64/mozilla/plugins/libflashplayer.so /usr/lib/mozilla/plugins/libflashplayer.so