User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:43.0) Gecko/20100101 Firefox/43.0 Build ID: 20150905030205 Steps to reproduce: Just watching YouTube videos in HTML5 format Actual results: Sometimes Nightly 43a1 totally freezes for whole minute or so (see first two screenshots), while FireFox.exe becomes 100% busy in its thread (see the third attachment, where 13% busy in hyper-threading mode for four-core CPU means 100% per thread). Expected results: Normal continuous operation without freeze

I have to add that this bug is not methodically reproducible, it happens at random times.

If you right-click on the playing video before it hangs and select 'stats for nerds' what does it say about the format, resolution, DASH, etc.?

Typical "video/mp4; codecs="avc1.640028""

this isn't enough information. Please provide the entire text thank you

Video ID: h1R2dW58x24 Dimensions: 854 x 480 * 1.3953487873077393 Resolution: 1280 x 720@24 Volume: 40% Stream Host: r5---sn-8ph2xajvh-axqe Stream Type: https CPN: AzMRqL6oYn1kYIDi Mime Type: video/mp4; codecs="avc1.640028" DASH: yes (137/140) Connection Speed: 26916 Kbps Dropped Frames: 0/91 ________________________________________________________ Since those freezes are not methodically reproducible, I am not sure how this would help, though.

The issue still is not going anywhere, even though I now have different OS, different video drivers version, and, of course, different version of FireFox. And it is as unpredictable as ever. My point, though, is that with e10s mode on, this should not be happening. GUI should be always absolute priority, not anything else (even if it happens because of synchronous GC calls).

Mass change P2 -> P3

Dderss, do you still see this when using newer version?

This has morphed into #Bug 1400000 lately, but it is not clear if it is related.

Morphed how? That you no longer see the symptoms of THIS bug?

The newer bug also manifests itself through freezes during YouTube (HTML5/H264) video playback just as this older bug. However, the scope of the newer bug is different as it is much clearer that it is a garbage leak issue rather than something video related primarily.