It first appeared in 17.0a1/20120816. The regression range is: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=7d4268f8884c&tochange=50e4ff05741e It's likely a regression from bug 743975. Signature nsBaseWidget::GetAccessible() More Reports Search UUID 90181ba8-b252-41f4-b5e3-e2c862120816 Date Processed 2012-08-16 19:53:46 Uptime 3664 Last Crash 1.0 hours before submission Install Age 3.6 hours since version was first installed. Install Time 2012-08-16 16:20:07 Product Firefox Version 17.0a1 Build ID 20120816030539 Release Channel nightly OS Windows NT OS Version 6.1.7601 Service Pack 1 Build Architecture x86 Build Architecture Info GenuineIntel family 6 model 26 stepping 4 Crash Reason EXCEPTION_ACCESS_VIOLATION_READ Crash Address 0x0 App Notes AdapterVendorID: 0x1002, AdapterDeviceID: 0x9440, AdapterSubsysID: 20071787, AdapterDriverVersion: 8.970.100.3000 Processor Notes WARNING: JSON file missing Add-ons EMCheckCompatibility True Adapter Vendor ID 0x1002 Adapter Device ID 0x9440 Total Virtual Memory 2147352576 Available Virtual Memory 1788301312 System Memory Use Percentage 78 Available Page File 927268864 Available Physical Memory 701054976 Frame Module Signature Source 0 xul.dll nsBaseWidget::GetAccessible widget/xpwidgets/nsBaseWidget.cpp:1388 1 xul.dll nsWindow::GetRootAccessible widget/windows/nsWindow.cpp:7361 2 xul.dll nsWindow::ProcessMessage widget/windows/nsWindow.cpp:5052 3 xul.dll nsWindow::WindowProcInternal widget/windows/nsWindow.cpp:4265 4 xul.dll CallWindowProcCrashProtected xpcom/base/nsCrashOnException.cpp:32 5 xul.dll nsWindow::WindowProc widget/windows/nsWindow.cpp:4207 ... More reports at: https://crash-stats.mozilla.com/report/list?signature=nsBaseWidget%3A%3AGetAccessible%28%29 https://crash-stats.mozilla.com/report/list?signature=nsBaseWidget%3A%3AGetAccessible

The null check in static nsIPresShell* GetPresShell(nsIWidget* aWidget, void* clientData) was removed by this revision: http://hg.mozilla.org/mozilla-central/rev/4aca82dc0d41. Furthermore, not all places that use mWidgetListener were null-checked thereafter.

Comment on attachment 652605 [details] [diff] [review] patch I think tnikkel is enough here.

Thank you!