I know this is a bit of a late reply, and hope SouthernGorilla has resolved the problem, but the solution carl0ski has suggested worked for me. I had the same problem as SouthernGorilla has (had). I use Fedora Core 3 with FireFox. My internet provider is a cable company, and I often visit their web site for the latest news. However, I have been having problem playing video on their website. Flash never worked for me with FireFox.
Yesterday, I decided to fix this problem even though Flash video wasn't so important to me, and came across with this thread. I tried carl0ski's solution since it seemed the easiest, and the problem was fixed. I do not know exactly what has been fixed, but my guess is that the fix has something to do with hidden (invisible) folder in my home directory called /home/<myusername>/.mozilla.
Originally when I installed Fedora Core on my machine, I installed FireFox 1.0.3, then I decided to install Japanese version of FireFox 2.0. While installing Japanese version, I think I installed it as my username instead of root. Then, when I installed Flash v. 9 later, I installed it as root. So, when I use Japanese FireFox, Flash 9 won't get recognized. I created a symbolic link under /usr/lib/firefox/plugins for Flash 9, but it never worked.
Yesterday, when I tried carl0ski's solution by installing FireFox under /home/<myusername> and installed Flash 9, my machine was able to play flash video. I have to point out that my Japanese version of FireFox has been installed under /usr/lib/firefox and Flash was also installed under /usr/lib/flash, but I didn't uninstall these when I tried carl0ski's solution yesterday. By logging in as my user name (instead of root), I simply installed FireFox under /home/<myusername> and installed Flash under /home/<myusername>/firefox, then I launched /home/<myusername>/firefox/firefox to confirm the Flash video can be played, then I simply deleted /home/<myusername>/firefox. Surprisingly, when I launched Japanese version of FireFox installed under /usr/lib/firefox, Flash was also working.
One thing I noticed was that during the Flash installation, installer was installing something to /home/<myusername>/.mozilla and warning me that I was not installing Flash as root. I simply ignored the warning and completed the installation, and Flash is now working. I am not a Linux expert, but I am a happy man now since Flash is working.