Build Identifier: https://hg.mozilla.org/integration/fx-team/rev/043466f5a7f1 Mozilla/5.0 (Windows NT 10.0; WOW64; rv:41.0) Gecko/20100101 Firefox/41.0 ID:20150610030358 This problem is reproducible since landing of Bug 1169911. Steps To Reproduce: 1. Enable TitleBar 2. Open Sidebar (Ctrl+B) 3. Enter fullscreen ( F11 ) Actual results: Background color problem of Sidebar Header See attached screenshot

It's interesting to me that this happens on win10 but not win8 (at least, I can't reproduce this on win8) when both are using the same CSS.

I can't reproduce this on my Surface Pro running win10, either. Alice, what graphics card/driver are you using on this machine (is it a VM? I can try and repro in my win10 vmware instance as soon as I'm done using it with win7 for something else...), and is there anything else I might be missing? I just downloaded the 64-bit opt build for the rev you mentioned from ftp, for my win10 testing. Does the order in which I enable the titlebar and the sidebar matter? If you quit and restart, does that make it go away? (Just trying to figure out why I'm not seeing the same thing here...)

Yes VM Steps 1 . VMWare player Host Wndows7sp1 x64 Guest Windows10Tp build10130 x64 2. Launch Firefox.exe from http://ftp.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/fx-team-win32/1433930638/ 3. And Follow STR in comment#0

* Titlebar should be enabled. * Sidebar should be opened. * Reproduced every after enter fullscreen. * Once unhide fullscreen toolbar then the problem is gone. * Exit and re-enter fullscreen then the problem re-appears sometimes(80% probability).

I can also reproduced on Win8.1(VM)

This only reproduces on my VM, and only when not in safe mode. It seems to have something to do with having accelerated graphics (D3D11 WARP) but no direct2d ("blocked for your graphics card because of unresolved driver issues"). If I restart in safe mode (turning off hwa entirely), the issue doesn't happen. I'll post about:support info shortly. --> over to graphics, because this probably isn't specific to the sidebar on win10/win8 on vmware even if we could wallpaper over that case with more CSS adjustments.

Graphics -------- Adapter Description: VMware SVGA 3D Adapter Drivers: vm3dum64 vm3dum Adapter RAM: 512 Asynchronous Pan/Zoom: none Device ID: 0x0405 Direct2D Enabled: Blocked for your graphics card because of unresolved driver issues. DirectWrite Enabled: false (10.0.10130.0) Driver Date: 7-29-2014 Driver Version: 8.14.1.51 GPU #2 Active: false GPU Accelerated Windows: 1/1 Direct3D 11 WARP (OMTC) Subsys ID: 040515ad Supports Hardware H264 Decoding: false Vendor ID: 0x15ad WebGL Renderer: Blocked for your graphics card because of unresolved driver issues. windowLayerManagerRemote: true AzureCanvasBackend: skia AzureContentBackend: cairo AzureFallbackCanvasBackend: cairo AzureSkiaAccelerated: 0 Milan, can you point to someone who can look into this further?

I'll leave this as needinfo on me, but I'm not prioritizing VM bugs at this point.

Setting priority to P4 due to this being a VM bug (could possibly go lower). If this was not a VM bug we (the Firefox desktop team) would mark it higher priority.

Is this bug still reproducible?

No longer reproduce on Windows10 RS1.