It's tricky to find a working setup for Flash these days, that doesn't make firefox pause for around 8 seconds when opening a web page containing Flash.
I use Ubuntu's xorg-server
(xorg-server_1.10.4-1ubuntu4.1.diff, without 191-Xorg-add-an-extra-module-path.patch, and with --enable-gestures
which is required for Ubuntu's patches to compile), with nvidia 285.05.09 - this works fine. My distro is, well, "custom", based on Lunar.
I tried xorg-server 1.11.3 only temporarily yesterday, because it just brought the 8-second Flash pause back.