[Affected versions]: Try build for Nightly 56 validation, here is the link to download it: https://queue.taskcluster.net/v1/task/HlGbN6cvT5KsaPcVa2e_Mw/runs/0/artifacts/public/build/target.dmg [Affected platforms]: Mac OS X 10.12 [Steps to reproduce]: 1. Go to Netflix and play a video 2. After the video starts move the mouse over the progress bar. [Expected result]: The progress bar doesn't flicker when you move the mouse over it. [Actual result]: The progress bar flickers. NOTE: Please see the attached video for a better understanding.