I discover the problem when I test Bug 1057775. Steps To Reproduce: 1. Open attachment 8477907 [details] of Bug 1057775 Actual Results: The video flicker Expected Results: No flicker. Chrome works fine. This is a regression since Firefox23. Regression window(m-c) Good: http://hg.mozilla.org/mozilla-central/rev/c9b8fdfe0299 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20130504 Firefox/23.0 ID:20130504032244 Bad: http://hg.mozilla.org/mozilla-central/rev/7ef3c04c7533 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20130504 Firefox/23.0 ID:20130504140045 Pushlog: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=c9b8fdfe0299&tochange=7ef3c04c7533 Regression window(m-c) Good: http://hg.mozilla.org/integration/mozilla-inbound/rev/f58eca3886bd Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20130504 Firefox/23.0 ID:20130504014744 Bad: http://hg.mozilla.org/integration/mozilla-inbound/rev/79a0efe06e37 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20130504 Firefox/23.0 ID:20130504031346 Pushlog: http://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=f58eca3886bd&tochange=79a0efe06e37 Suspect: Bug 847267 - Enable DXVA2 on Windows Vista+ to accelerate H.264 video decoding Graphics -------- Adapter Description: ATI Radeon HD 4300/4500 Series Adapter Drivers: aticfx64 aticfx64 aticfx32 aticfx32 atiumd64 atidxx64 atiumdag atidxx32 atiumdva atiumd6a atitmm64 Adapter RAM: 512 ClearType Parameters: Gamma: 2200 Pixel Structure: R ClearType Level: 50 Enhanced Contrast: 200 Device ID: 0x954f Direct2D Enabled: true DirectWrite Enabled: true (6.2.9200.16571) Driver Date: 4-29-2013 Driver Version: 8.970.100.1100 GPU #2 Active: false GPU Accelerated Windows: 1/1 Direct3D 11 (OMTC) Subsys ID: 00000000 Vendor ID: 0x1002 WebGL Renderer: Google Inc. -- ANGLE (ATI Radeon HD 4300/4500 Series Direct3D9Ex vs_3_0 ps_3_0) windowLayerManagerRemote: true AzureCanvasBackend: direct2d AzureContentBackend: direct2d AzureFallbackCanvasBackend: cairo AzureSkiaAccelerated: 0

I cannot reproduce on Firefox35, esr31