This may be related to bug 1183288 or bug 1195132, but seems worth filing as its own bug. On a new Microsoft Surface Book running Windows 10, running Nightly, with e10s off because it says there's an accessibility tool active, I occasionally (maybe 10% of the time) see context menus misdrawn -- they've got a black and white grid covering part of the context menu. I haven't seen similar glitches anywhere other than context menus.
As in bug 1195132, does setting layers.offmainthreadcomposition.enabled = false make the problem disappear?
I think it does disappear. At least, I haven't seen it appear yet. (Though given the rate at which it occurs -- and the somewhat clumpy patterns of occurrences -- I can't quite be 100% sure.)
Still haven't seen it, which I think is reasonably conclusive at this point.
Created attachment 8702148 [details] screenshot: bug also shows up for tab dropdown I wonder if this is related to nsWindow::ComputeShouldAccelerate having conditions based on IsPopup(). (But not that the windows nsWindow::ShouldUseOffMainThreadCompositing doesn't have that condition.)