STR: 1. Visit a YouTube video with HTML5 video enabled (whether turned on nicely or forced) 2. Play 3. Observe black flicker every half-second or so Reproducible: always I'm on a Dell XPS 13, Windows 7, and a Nightly built May 28th. I've confirmed that setting layers.offmainthreadcomposition.enabled to false causes this issue to go away. I haven't tested whether or how Hardware Acceleration affects this. Possibly related to bug #1016408.

Nical, have a look at this one. Maybe you can repro?

So far doesn't repro on my computer. Alex, can you copy-paste the content of about:support here?

I get flickering on pretty much every HTML5 YouTube video if I speed up playback to 1.5x or 2x. Same thing in a clean profile, so I don't think it's my extensions.

Aaaaaand looks like this was caused by an addon. (Why I didn't test in a clean profile, I don't know.) I'll see if I can nail down which one, but looks like this bug is INVALID. Allan: feel free to file a new bug.

Nope, just reproduced on a clean profile (the problem was that I wasn't getting put in the HTML5 Player when I tried to reproduce). Here's about:support. It's worth noting that I _believe_ this is a regression. If wanted, I'm willing to try to find a regression range.

I can reproduce it reliably with these steps: 0. Enable OMTC. 1. Load https://bug1031319.bugzilla.mozilla.org/attachment.cgi?id=8447175. 2. Make sure video control is set as shown from context menu. 3. While video is playing, move cursor rapidly in and out of the video region. Result: Video flickers a few times during playback.