I am running OS X 10.11.6 and I have a strange problem with video. When I watch youtube video in FireFox (50.1.0, updated often), I see video flickering (fast blink) whenever the progress bar is shown. That includes when I move my mouse or kept my mouse pointer on the progress bar.
It seems that whenever there is an image overlay, the video will flicker. This does not happen in Safari but happens when I watch Amazon video in Safari. This problem has been bothering me for months. I cannot figure out how to resolve it. Please help!
Edit: I'm using the native HTML5 codec. Flash is disabled.
Here is an example of video causing problem: https://www.youtube.com/watch?v=coDff5RLIas
However, I noticed that not all video flicker as bad. Here is an example that seems to only flicker in full screen: https://www.youtube.com/watch?v=coDff5RLIas