Right after: TEST-PASS | chrome://mochitests/content/browser/browser/components/preferences/tests/browser_privacypane_1.js | the clear data settings button should exist (and then a few additional times later), I see: ###!!! ASSERTION: XPConnect is being called on a scope without a 'Components' property! (stack follows): 'Error', file /builds/slave/tryserver-linux-debug/build/js/src/xpconnect/src/xpcwrappednativescope.cpp, line 781 The C++ stack is: DEBUG_CheckForComponentsInScope [js/src/xpconnect/src/xpcwrappednativescope.cpp:782] XPCWrappedNativeScope::FindInJSObjectScope [js/src/xpconnect/src/xpcwrappednativescope.cpp:857] XPCConvert::NativeInterface2JSObject [js/src/xpconnect/src/xpcconvert.cpp:1164] XPCConvert::NativeData2JS [js/src/xpconnect/src/xpcconvert.cpp:489] XPCConvert::NativeData2JS [js/src/xpconnect/src/xpcprivate.h:3231] nsXPCWrappedJSClass::CallMethod [js/src/xpconnect/src/xpcwrappedjsclass.cpp:1587] nsXPCWrappedJS::CallMethod [js/src/xpconnect/src/xpcwrappedjs.cpp:588] PrepareAndDispatch [xpcom/reflect/xptcall/src/md/unix/xptcstubs_gcc_x86_unix.cpp:95] nsPrefBranch::NotifyObserver [modules/libpref/src/nsPrefBranch.cpp:731] pref_DoCallback [modules/libpref/src/prefapi.cpp:970] pref_HashPref [modules/libpref/src/prefapi.cpp:827] PREF_SetBoolPref [modules/libpref/src/prefapi.cpp:312] nsPrefBranch::SetBoolPref [modules/libpref/src/nsPrefBranch.cpp:182] nsPrefService::SetBoolPref [modules/libpref/src/nsPrefService.h:62] xptiInterfaceEntry::EnsureResolved [xpcom/reflect/xptinfo/src/xptiprivate.h:264] CallMethodHelper::Invoke [js/src/xpconnect/src/xpcwrappednative.cpp:3042] CallMethodHelper::Call [js/src/xpconnect/src/xpcwrappednative.cpp:2304] XPCWrappedNative::CallMethod [js/src/xpconnect/src/xpcwrappednative.cpp:2268] XPC_WN_CallMethod [js/src/xpconnect/src/xpcwrappednativejsops.cpp:1594] js::CallJSNative [js/src/jscntxtinlines.h:684] js::Interpret [js/src/jsinterp.cpp:4743] js::RunScript [js/src/jsinterp.cpp:657] js::Invoke [js/src/jsinterp.cpp:737] js::ExternalInvoke [js/src/jsinterp.cpp:858] js::ExternalInvoke [js/src/jsinterp.h:955] js::ExternalGetOrSet [js/src/jsinterp.cpp:898] js::Shape::set [js/src/jsscopeinlines.h:266] js_SetPropertyHelper [js/src/jsobj.cpp:5310] js::Interpret [js/src/jsinterp.cpp:4445] js::RunScript [js/src/jsinterp.cpp:657] js::Invoke [js/src/jsinterp.cpp:737] js::ExternalInvoke [js/src/jsinterp.cpp:858] js::ExternalInvoke [js/src/jsinterp.h:955] js::ExternalGetOrSet [js/src/jsinterp.cpp:898] js::Shape::set [js/src/jsscopeinlines.h:266] js_SetPropertyHelper [js/src/jsobj.cpp:5310] js::Interpret [js/src/jsinterp.cpp:4445] js::RunScript [js/src/jsinterp.cpp:657] js::Invoke [js/src/jsinterp.cpp:737] js::ExternalInvoke [js/src/jsinterp.cpp:858] js::ExternalInvoke [js/src/jsinterp.h:955] JS_CallFunctionValue [js/src/jsapi.cpp:4973] nsJSContext::CallEventHandler [dom/base/nsJSEnvironment.cpp:2177] nsJSEventListener::HandleEvent [dom/src/events/nsJSEventListener.cpp:228] nsEventListenerManager::HandleEventSubType [content/events/src/nsEventListenerManager.cpp:1114] nsEventListenerManager::HandleEventInternal [content/events/src/nsEventListenerManager.cpp:1211] nsEventListenerManager::HandleEvent [content/events/src/nsEventListenerManager.h:146] nsEventTargetChainItem::HandleEvent [content/events/src/nsEventDispatcher.cpp:213] nsEventTargetChainItem::HandleEventTargetChain [content/events/src/nsEventDispatcher.cpp:343] nsEventDispatcher::Dispatch [content/events/src/nsEventDispatcher.cpp:628] nsEventDispatcher::DispatchDOMEvent [content/events/src/nsEventDispatcher.cpp:691] nsEventListenerManager::DispatchEvent [content/events/src/nsEventListenerManager.cpp:1328] nsDOMEventRTTearoff::DispatchEvent [content/base/src/nsGenericElement.cpp:1970] nsContentUtils::DispatchXULCommand [content/base/src/nsContentUtils.cpp:5522] nsXULElement::DoCommand [content/xul/content/src/nsXULElement.cpp:2155] nsIDOMXULElement_DoCommand [dom_quickstubs.cpp:25006] js::CallJSNative [js/src/jscntxtinlines.h:684] js::Interpret [js/src/jsinterp.cpp:4743] js::RunScript [js/src/jsinterp.cpp:657] js::Invoke [js/src/jsinterp.cpp:737] js::ExternalInvoke [js/src/jsinterp.cpp:858] js::ExternalInvoke [js/src/jsinterp.h:955] JS_CallFunctionValue [js/src/jsapi.cpp:4973] nsXPCWrappedJSClass::CallMethod [js/src/xpconnect/src/xpcwrappedjsclass.cpp:1694] nsXPCWrappedJS::CallMethod [js/src/xpconnect/src/xpcwrappedjs.cpp:588] PrepareAndDispatch [xpcom/reflect/xptcall/src/md/unix/xptcstubs_gcc_x86_unix.cpp:95] nsEventListenerManager::HandleEventSubType [content/events/src/nsEventListenerManager.cpp:1114] nsEventListenerManager::HandleEventInternal [content/events/src/nsEventListenerManager.cpp:1211] nsEventListenerManager::HandleEvent [content/events/src/nsEventListenerManager.h:146] nsEventTargetChainItem::HandleEvent [content/events/src/nsEventDispatcher.cpp:213] nsEventTargetChainItem::HandleEventTargetChain [content/events/src/nsEventDispatcher.cpp:343] nsEventDispatcher::Dispatch [content/events/src/nsEventDispatcher.cpp:628] DocumentViewerImpl::LoadComplete [layout/base/nsDocumentViewer.cpp:1034] nsDocShell::EndPageLoad [docshell/base/nsDocShell.cpp:6028] nsDocShell::OnStateChange [docshell/base/nsDocShell.cpp:5881] nsDocLoader::FireOnStateChange [uriloader/base/nsDocLoader.cpp:1318] nsDocLoader::doStopDocumentLoad [uriloader/base/nsDocLoader.cpp:953] nsDocLoader::DocLoaderIsEmpty [uriloader/base/nsDocLoader.cpp:820] nsDocLoader::OnStopRequest [uriloader/base/nsDocLoader.cpp:705] nsLoadGroup::RemoveRequest [netwerk/base/src/nsLoadGroup.cpp:680] nsDocument::DoUnblockOnload [content/base/src/nsDocument.cpp:7269] nsDocument::UnblockOnload [content/base/src/nsDocument.cpp:7210] nsBindingManager::DoProcessAttachedQueue [content/xbl/src/nsBindingManager.cpp:999] nsRunnableMethodImpl<void (nsBindingManager::*)(), true>::Run [nsThreadUtils.h:346] nsThread::ProcessNextEvent [xpcom/threads/nsThread.cpp:626] NS_ProcessNextEvent_P [nsThreadUtils.cpp:250] mozilla::ipc::MessagePump::Run [ipc/glue/MessagePump.cpp:110] MessageLoop::RunInternal [ipc/chromium/src/base/message_loop.cc:220] MessageLoop::RunHandler [ipc/chromium/src/base/message_loop.cc:203] MessageLoop::Run [ipc/chromium/src/base/message_loop.cc:176] nsBaseAppShell::Run [widget/src/xpwidgets/nsBaseAppShell.cpp:187] nsAppStartup::Run [toolkit/components/startup/src/nsAppStartup.cpp:191] XRE_main [toolkit/xre/nsAppRunner.cpp:3691] main [browser/app/nsBrowserApp.cpp:158] The JS stack at the time of the assertion is: The current JS stack is: JSStackFrame at 0xb2dfd2e8 callee fun: <function set_valueFromPreferences at 0xaf449188 (JSFunction at 0xaf6b3f50)> file chrome://global/content/bindings/preferences.xml line 325 pc = 0xaab74bc current op: call slots: 0xb2dfd318 sp: 0xb2dfd350 = slots + 7 0xb2dfd318: undefined 0xb2dfd320: undefined 0xb2dfd328: undefined 0xb2dfd330: undefined 0xb2dfd338: <XPCWrappedNative_NoHelper object at 0xaf4041c0> 0xb2dfd340: "browser.privatebrowsing.autostart" 0xb2dfd348: false actuals: 0xb2dfd2e0 (1) formals: 0xb2dfd2e0 (1) this: <XULElement object at 0xaf4497e0> rval: undefined flags: scopeChain: (JSObject *) 0xaf45a370 JSStackFrame at 0xb2dfd290 callee fun: <function _setValue at 0xaf4b3dc8 (JSFunction at 0xaf6b3af0)> file chrome://global/content/bindings/preferences.xml line 158 pc = 0xc835c12 current op: setprop slots: 0xb2dfd2c0 sp: 0xb2dfd2e8 = slots + 5 0xb2dfd2c0: <XULElement object at 0xaf4497e0> 0xb2dfd2c8: false 0xb2dfd2d0: <function set_valueFromPreferences at 0xaf449188 (JSFunction at 0xaf6b3f50)> 0xb2dfd2d8: <XULElement object at 0xaf4497e0> 0xb2dfd2e0: false actuals: 0xb2dfd280 (2) formals: 0xb2dfd280 (2) this: <XULElement object at 0xaf4497e0> rval: undefined flags: scopeChain: (JSObject *) 0xaf45a370 JSStackFrame at 0xb2dfd240 callee fun: <function set_value at 0xaf4b3e38 (JSFunction at 0xaf6b3b90)> file chrome://global/content/bindings/preferences.xml line 0 pc = 0xc4b5ba8 current op: call slots: 0xb2dfd270 sp: 0xb2dfd290 = slots + 4 0xb2dfd270: <function _setValue at 0xaf4b3dc8 (JSFunction at 0xaf6b3af0)> 0xb2dfd278: <XULElement object at 0xaf4497e0> 0xb2dfd280: false 0xb2dfd288: true actuals: 0xb2dfd238 (1) formals: 0xb2dfd238 (1) this: <XULElement object at 0xaf4497e0> rval: undefined flags: scopeChain: (JSObject *) 0xaf45a370 JSStackFrame at 0xb2dfd1d8 callee fun: <function PPP_updateHistoryModePrefs at 0xaf4b3038 (JSFunction at 0xaa80ed70)> file chrome://browser/content/preferences/privacy.js line 127 pc = 0xacce683 current op: setprop slots: 0xb2dfd208 sp: 0xb2dfd240 = slots + 7 0xb2dfd208: <XULElement object at 0xaf4497e0> 0xb2dfd210: undefined 0xb2dfd218: <XULElement object at 0xaf4497e0> 0xb2dfd220: false 0xb2dfd228: <function set_value at 0xaf4b3e38 (JSFunction at 0xaf6b3b90)> 0xb2dfd230: <XULElement object at 0xaf4497e0> 0xb2dfd238: false actuals: 0xb2dfd1d8 (0) formals: 0xb2dfd1d8 (0) this: <Object at 0xaf45a5a0> rval: undefined flags: scopeChain: (JSObject *) 0xaf45a370 JSStackFrame at 0xb2dfd198 callee fun: <function oncommand at 0xaf436b60 (JSFunction at 0xa9c551e0)> file chrome://browser/content/preferences/preferences.xul line 1 pc = 0xcc2a404 current op: call slots: 0xb2dfd1c8 sp: 0xb2dfd1d8 = slots + 2 0xb2dfd1c8: <function PPP_updateHistoryModePrefs at 0xaf4b3038 (JSFunction at 0xaa80ed70)> 0xb2dfd1d0: <Object at 0xaf45a5a0> actuals: 0xb2dfd190 (1) formals: 0xb2dfd190 (1) this: <XULElement object at 0xaf457348> rval: undefined flags: scopeChain: (JSObject *) 0xaf457348 JSStackFrame at 0xb2dfd140 callee fun: <function controlChanged at 0xaa8eb960 (JSFunction at 0xaa8eb960)> file chrome://mochitests/content/browser/browser/components/preferences/tests/browser_privacypane_1.js -> file:///tmp/tmp9hWEkc/mochikit-1.tmp/privacypane_tests.js line 64 pc = 0xb8995ae current op: call slots: 0xb2dfd170 sp: 0xb2dfd198 = slots + 5 0xb2dfd170: <function doCommand at 0xaf6cbf50 (JSFunction at 0xaf6cbf50)> 0xb2dfd178: <XULElement object at 0xaf457348> 0xb2dfd180: <function oncommand at 0xaf436b60 (JSFunction at 0xa9c551e0)> 0xb2dfd188: <XULElement object at 0xaf457348> 0xb2dfd190: <XULCommandEvent object at 0xaf436c78> actuals: 0xb2dfd138 (1) formals: 0xb2dfd138 (1) this: <Object at 0xa1e20d38> rval: undefined flags: scopeChain: (JSObject *) 0xa1e20d38 JSStackFrame at 0xb2dfd090 callee fun: <function test_dependent_elements at 0xaa8eba00 (JSFunction at 0xaa8eba00)> file chrome://mochitests/content/browser/browser/components/preferences/tests/browser_privacypane_1.js -> file:///tmp/tmp9hWEkc/mochikit-1.tmp/privacypane_tests.js line 88 pc = 0xd883744 current op: call slots: 0xb2dfd0c0 sp: 0xb2dfd140 = slots + 16 0xb2dfd0c0: <XULElement object at 0xaf457348> 0xb2dfd0c8: <XULElement object at 0xaf481188> 0xb2dfd0d0: <Array object at 0xaf6ac7b8> 0xb2dfd0d8: <Array object at 0xaf436a10> 0xb2dfd0e0: <XULElement object at 0xaf481b98> 0xb2dfd0e8: <XULElement object at 0xaf4a6118> 0xb2dfd0f0: <XULElement object at 0xaf4a64d0> 0xb2dfd0f8: <XULElement object at 0xaf481540> 0xb2dfd100: <XULElement object at 0xaf4815b0> 0xb2dfd108: <XULElement object at 0xaf4815e8> 0xb2dfd110: <XULElement object at 0xaf4a6508> 0xb2dfd118: <function expect_disabled at 0xaf436968 (JSFunction at 0xaa8ebaf0)> 0xb2dfd120: <function check_independents at 0xaf4369a0 (JSFunction at 0xaa8ebb90)> 0xb2dfd128: <function controlChanged at 0xaa8eb960 (JSFunction at 0xaa8eb960)> 0xb2dfd130: <Object at 0xa1e20d38> 0xb2dfd138: <XULElement object at 0xaf457348> actuals: 0xb2dfd088 (1) formals: 0xb2dfd088 (1) this: undefined rval: undefined flags: scopeChain: (JSObject *) 0xa1e20d38 JSStackFrame at 0xb2dfd048 callee fun: <unnamed function at 0xabd017e0 (JSFunction at 0xaa8eb910)> file chrome://mochitests/content/browser/browser/components/preferences/tests/browser_privacypane_1.js -> file:///tmp/tmp9hWEkc/mochikit-1.tmp/privacypane_tests.js line 45 pc = 0xb59b156 current op: call slots: 0xb2dfd078 sp: 0xb2dfd090 = slots + 3 0xb2dfd078: <function test_dependent_elements at 0xaa8eba00 (JSFunction at 0xaa8eba00)> 0xb2dfd080: undefined 0xb2dfd088: <Proxy object at 0xa1ef5d80> actuals: 0xb2dfd030 (1) formals: 0xb2dfd048 (0) argsobj: <Arguments object at 0xaf436930> this: <Proxy object at 0xa1ef5d80> rval: undefined flags: scopeChain: (JSObject *) 0xabd017a8 And the object whose scope lacks a 'Components' property is: object 0xab01c460 class 0x34a4380 Object flags: none properties: enumerate "observe": slot 1 enumerate "QueryInterface": slot 0 proto <Object at 0xaf7b22a8> parent <ChromeWindow object at 0xaf7b2258> slots: 0 = <function XPCOMUtils_QueryInterface at 0xab01c8f8 (JSFunction at 0xb2c0bc80)> 1 = <function PPP_observe at 0xab01c930 (JSFunction at 0xaa80eeb0)> which is the autoStartPrivateBrowsingObserver object in browser/components/preferences/privacy.js. As far as I can tell, privacy.js never calls removeObserver on this observer. (I'm a bit confused as to what this code is doing, and why this observer is associated with pref window code.)

Calls to this observer are responsible for 177 assertions during mochitest-other on Linux.

Comment on attachment 493428 [details] [diff] [review] Patch (v1) Per IRC, let's just make uninitAutoStartPrivateBrowsingObserver.bind(this) the unload handler directly, and maybe give it a shorter name like removePBObserver or something. r=me with that.

Comments addressed.