It first appeared in 14.0a1/20120325. The regression range might be (low volume): http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=df1f94b2bdee&tochange=20a01901480f Signature nsHttpConnectionMgr::PostEvent(void ( nsHttpConnectionMgr::*)(int, void*), int, void*) More Reports Search UUID c69ba764-418c-419f-9123-7a5a62120326 Date Processed 2012-03-26 05:38:28 Uptime 1918 Last Crash 32.3 minutes before submission Install Age 43.9 minutes since version was first installed. Install Time 2012-03-26 04:50:24 Product Firefox Version 14.0a1 Build ID 20120325031055 Release Channel nightly OS Windows NT OS Version 5.1.2600 Service Pack 3 Build Architecture x86 Build Architecture Info GenuineIntel family 6 model 37 stepping 5 Crash Reason EXCEPTION_ACCESS_VIOLATION_EXEC Crash Address 0x65747369 App Notes AdapterVendorID: 0x10de, AdapterDeviceID: 0x0a2c, AdapterSubsysID: 1521103c, AdapterDriverVersion: 6.14.12.6128 D3D10 Layers? D3D10 Layers- D3D9 Layers? D3D9 Layers+ EMCheckCompatibility True Total Virtual Memory 2147352576 Available Virtual Memory 1787899904 System Memory Use Percentage 33 Available Page File 4367712256 Available Physical Memory 2135650304 Frame Module Signature [Expand] Source 0 @0x65747369 1 xul.dll nsHttpConnectionMgr::PostEvent netwerk/protocol/http/nsHttpConnectionMgr.cpp:205 2 xul.dll nsHttpConnectionMgr::CancelTransaction netwerk/protocol/http/nsHttpConnectionMgr.cpp:319 3 xul.dll nsHttpChannel::Cancel netwerk/protocol/http/nsHttpChannel.cpp:3804 4 xul.dll nsHttpChannel::ProcessFailedSSLConnect netwerk/protocol/http/nsHttpChannel.cpp:883 5 xul.dll nsHttpChannel::ProcessResponse netwerk/protocol/http/nsHttpChannel.cpp:997 6 xul.dll nsHttpChannel::OnStartRequest netwerk/protocol/http/nsHttpChannel.cpp:4316 7 xul.dll nsInputStreamPump::OnStateStart netwerk/base/src/nsInputStreamPump.cpp:444 8 xul.dll nsInputStreamPump::OnInputStreamReady netwerk/base/src/nsInputStreamPump.cpp:399 9 xul.dll nsInputStreamReadyEvent::Run xpcom/io/nsStreamUtils.cpp:114 10 xul.dll nsThread::ProcessNextEvent xpcom/threads/nsThread.cpp:656 11 xul.dll mozilla::ipc::MessagePump::Run ipc/glue/MessagePump.cpp:134 12 xul.dll MessageLoop::RunHandler ipc/chromium/src/base/message_loop.cc:201 13 xul.dll MessageLoop::Run ipc/chromium/src/base/message_loop.cc:175 14 xul.dll nsBaseAppShell::Run widget/xpwidgets/nsBaseAppShell.cpp:189 15 xul.dll nsAppShell::Run widget/windows/nsAppShell.cpp:267 16 xul.dll nsAppStartup::Run toolkit/components/startup/nsAppStartup.cpp:295 17 xul.dll XRE_main toolkit/xre/nsAppRunner.cpp:3703 ... More reports at: https://crash-stats.mozilla.com/report/list?signature=nsHttpConnectionMgr%3A%3APostEvent%28void+%28+nsHttpConnectionMgr%3A%3A*%29%28int%2C+void*%29%2C+int%2C+void*%29

Patrick - is this a regression from your pipelining patches?

see stack of comment 15 in 741056 - dup.