If you just want to have entrance to webbsites just accepting e.g flash 9.069, you can edit pluginreg.dat in the Firefox folder. Change value to 9.0 r 69 as below. Restart FF. There is an earlier thread about it. The changes does not disappear after reboot. I do not understand german but followed a link to www.myvideo.de. Befor change I wasn't allowed, after change I could watch movies (that workes with flash 7of course) without problems.

[PLUGINS]
D:\HOME\DEFAULT\Mozilla\plugins\npswf2.dll:$
:$
1067622360000:1:7:$
Shockwave Flash 9.0 r69<br>OS/2 Runtime Environment &#169; 2003 <a href=http://www.innotek.de>InnoTek&#174; Systemberatung </a>:$
Shockwave Flash:$
1
0:application/x-shockwave-flash:Shockwave Flash:swf:$