Get weird flicker in flash videos

I’ve noticed a weird thing with flash:

  1. When playing flash videos in firefox, they’ll flicker with black screen flashing for a split second over the video

(This continues throughout the video)

  1. However, if I do either of the following, the flicker goes away (only while doing one of these actions):

a. Continually move the mouse over the video (i.e. move back and forth in a “mouseover”)

b. Put the mouse over the scrubber circle (which shows time lapsed and allows dragging to change location in video) such that the “hand” cursor appears. Once the cursor changes back to a pointer, it flickers again. but as long as I move the mouse over the scrubber circle, it’ll stop the flickering (even without moving the mouse anymore) until the circle passes beyond the cursor again.

Any ideas how to stop the flickering?

Do you have the driver for your video card installed?
Does this happen in other browsers? Chrome, Opera?
Flash version?

Does it stop if you disable desktop effects/compositing?