When moving the browsers window in which a video is playing to the second display, the videos brightness or gamma changes. This results in a too bright video on my second display. When moving it back to the first display it changes back (to normal). If the video is paused it does not change brightness. But as soon as you resume it the brightness changes. Only the brightness of the video changes not of the whole site. This happens only if using a HTML5 video player. When using flash it does not happen. This happens only in firefox, other browser do not behave like this. I noticed this first after the firefox update to 55.0.3 which was today. Im using win10 pro as OS.