Flash has worked previously on Karmic x64 by installing the 64 bit version of Flash 10.0 r32 alpha from Adobe Labs but ceased to work after update. White screen appears only.
Goto Firefox -> Tools -> Add-ons -> Plugins
There will be two entries for Shockwave Flash: 10.0 r32 and 10.0 r42.
Disable Shockwave Flash 10.0 r32 and restart Firefox.
Test in Youtube and/or Facebook videos should work again.
