Mozilla/5.0 (Windows NT 6.1; rv:2.0b8pre) Gecko/20101209 Firefox/4.0b8pre I been noticing this with D3D9 using this URL - (http://thebubble.msn.com) on a 1024x768 screen in maximized mode while testing bug 579597 (large enough the plugin overlaps the scrollbar, scrolling up and down I can trigger it) Horizontal scrollbar almost appears to be transparent when it first loads the plugin. But then I noticed it will occur with Youtube WebM video as well if the window is sized correctly. Basically the horizontal scrollbar is covered up by the flash plugin or WebM video on Youtube if it bisects the plugin area - basically I make the window small enough so that the horizontal scrollbar overlaps. You'll see by the attached screenshot, it doesn't even have to be playing for this to happen. Since it will be that way once the video stops. Not a problem: Its not a problem if I disable D3D9. Though Youtube Flash doesn't look like it is affected. Adapter Description NVIDIA GeForce 7050 / NVIDIA nForce 610i Vendor ID10de Device ID07e3 Adapter RAM 256 Adapter Drivers nvd3dum Driver Version 8.17.12.6099 Driver Date 10-16-2010 Direct2D Enabled true DirectWrite Enabled true GPU Accelerated Windows 1/1 Direct3D 9

WebM video link I been testing with: http://www.youtube.com/watch?v=BH0BNbwqNK8&webm=1&html5=1

Regression window: Works: http://hg.mozilla.org/mozilla-central/rev/29d2042e54aa Mozilla/5.0 (Windows NT 5.1; rv:2.0b8pre) Gecko/20101021 Firefox/4.0b8pre ID:20101021134825 Fails: http://hg.mozilla.org/mozilla-central/rev/f4a06cca9fb9 Mozilla/5.0 (Windows NT 5.1; rv:2.0b8pre) Gecko/20101021 Firefox/4.0b8pre ID:20101021143501 Pushlog: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=29d2042e54aa&tochange=f4a06cca9fb9 Regressed by:73f8c0079bc1 Bas Schouten — Bug 584494: Avoid creating intermediate surfaces in D3D9 layers. r=roc a=blocking-betaN And maybe related to Bug 614651 - Canvas element(Google images) show through the add-on bar and horizontal scrollbar with D3D9:on

Whats interesting is that vertical scrollbar doesn't have this problem.

It makes me sad, but it's only the horizontal scrollbar. I want this fixed, but I think we can release without this fix.

I think we should try to fix this. It's unlikely to be just the horizontal scrollbar, it's likely to be a fundamental layer rendering bug.

I can reproduce this. The regression window is certainly interesting. I agree with roc that this is indicative of a more fundamental rendering issue.

This will be fixed by bug 614651.

Verified this is fixed.