I don't think it is media bug. Probably it might be related to DOM. This problem happens on my macbook pro (10.12.6) with the latest nightly, 57.0a1 (2017-08-04) (64-bit).
Cannot see this problem with a clear profile. I am going to check what is inside my profile.
Status: NEW → RESOLVED
Last Resolved: a year ago
Resolution: --- → DUPLICATE
Duplicate of bug: 1363234
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