I see this on every Hulu video, using the 64-bit flash plugin on x86_64.
Fortunately, I can still control the video using the keyboard - for
example, space bar to pause/play and up/down arrows to control the
volume. I think but am not absolutely sure that the problem started
after installing Nvidia's video driver from Rpmfusion (akmod-nvidia,
adding the nouveau.modeset=0 kernel option, and running "setsebool -P
allow_execstack on").