It happens while loading http://youtube.com/ in debug mode, sometimes. ASSERTION FAILED: firstProperty == lastProperty (gdb) p firstProperty $1 = 26 (gdb) p lastProperty $2 = 416 #0 WTFCrash () at ../../Source/WTF/wtf/Assertions.cpp:255 #1 0x00007febbba58423 in WebCore::StyleResolver::applyCascadedPropertiesImpl<(WebCore::StyleResolver::CustomPropertyCycleTracking)0> (this=0x7feaa44b4500, firstProperty=26, lastProperty=416, state=...) at ../../Source/WebCore/css/StyleResolver.cpp:2399 #2 0x00007febbba49fb7 in WebCore::StyleResolver::applyCascadedProperties (this=0x7feaa44b4500, firstProperty=26, lastProperty=416, state=...) at ../../Source/WebCore/css/StyleResolver.cpp:2376 #3 0x00007febbba46457 in WebCore::StyleResolver::applyMatchedProperties (this=0x7feaa44b4500, matchResult=..., element=..., shouldUseMatchedPropertiesCache=WebCore::StyleResolver::UseMatchedPropertiesCache) at ../../Source/WebCore/css/StyleResolver.cpp:1434 #4 0x00007febbba4164c in WebCore::StyleResolver::styleForElement (this=0x7feaa44b4500, element=..., parentStyle=0x7feb08313300, parentBoxStyle=0x7feb08313300, matchingBehavior=WebCore::RuleMatchingBehavior::MatchAllRules, selectorFilter=0x7feb4e4ed410) at ../../Source/WebCore/css/StyleResolver.cpp:397 #5 0x00007febbcb2620b in WebCore::Style::TreeResolver::styleForElement (this=0x7ffd51766030, element=..., inheritedStyle=...) at ../../Source/WebCore/style/StyleTreeResolver.cpp:131 #6 0x00007febbcb265aa in WebCore::Style::TreeResolver::resolveElement (this=0x7ffd51766030, element=...) at ../../Source/WebCore/style/StyleTreeResolver.cpp:192 #7 0x00007febbcb27acc in WebCore::Style::TreeResolver::resolveComposedTree (this=0x7ffd51766030) at ../../Source/WebCore/style/StyleTreeResolver.cpp:489 #8 0x00007febbcb27ee4 in WebCore::Style::TreeResolver::resolve (this=0x7ffd51766030) at ../../Source/WebCore/style/StyleTreeResolver.cpp:547 #9 0x00007febbbb624ae in WebCore::Document::resolveStyle (this=0x7feb33402fd0, type=WebCore::Document::ResolveStyleType::Normal) at ../../Source/WebCore/dom/Document.cpp:1921 #10 0x00007febbbb62ceb in WebCore::Document::updateStyleIfNeeded (this=0x7feb33402fd0) at ../../Source/WebCore/dom/Document.cpp:2050 #11 0x00007febbbb62e53 in WebCore::Document::updateLayout (this=0x7feb33402fd0) at ../../Source/WebCore/dom/Document.cpp:2087 #12 0x00007febbc9ad4e7 in WebCore::RenderView::hitTest (this=0x7feb33200768, request=..., location=..., result=...) at ../../Source/WebCore/rendering/RenderView.cpp:147 #13 0x00007febbc9ad4b7 in WebCore::RenderView::hitTest (this=0x7feb33200768, request=..., result=...) at ../../Source/WebCore/rendering/RenderView.cpp:142 #14 0x00007febbbb69212 in WebCore::Document::prepareMouseEvent (this=0x7feb33402fd0, request=..., documentPoint=..., event=...) at ../../Source/WebCore/dom/Document.cpp:3723 #15 0x00007febbc2e9bc5 in WebCore::EventHandler::handleMousePressEvent (this=0x7feba24c5480, platformMouseEvent=...) at ../../Source/WebCore/page/EventHandler.cpp:1705 #16 0x00007febbcb16f1e in WebCore::UserInputBridge::handleMousePressEvent (this=0xbe5700, mouseEvent=...) at ../../Source/WebCore/replay/UserInputBridge.cpp:57 #17 0x00007febba8c63b5 in WebKit::handleMouseEvent (mouseEvent=..., page=0x7feb543fa600) at ../../Source/WebKit/WebProcess/WebPage/WebPage.cpp:2483 #18 0x00007febba8c6635 in WebKit::WebPage::mouseEvent (this=0x7feb543fa600, mouseEvent=...) at ../../Source/WebKit/WebProcess/WebPage/WebPage.cpp:2550 #19 0x00007febb9f0f93e in IPC::callMemberFunctionImpl<WebKit::WebPage, void (WebKit::WebPage::*)(WebKit::WebMouseEvent const&), std::tuple<WebKit::WebMouseEvent>, 0ul> (object=0x7feb543fa600, function= (void (WebKit::WebPage::*)(WebKit::WebPage * const, const WebKit::WebMouseEvent &)) 0x7febba8c6492 <WebKit::WebPage::mouseEvent(WebKit::WebMouseEvent const&)>, args=...) at ../../Source/WebKit/Platform/IPC/HandleMessage.h:41 #20 0x00007febb9f0c50c in IPC::callMemberFunction<WebKit::WebPage, void (WebKit::WebPage::*)(WebKit::WebMouseEvent const&), std::tuple<WebKit::WebMouseEvent>, std::integer_sequence<unsigned long, 0ul> > ( args=..., object=0x7feb543fa600, function=(void (WebKit::WebPage::*)(WebKit::WebPage * const, const WebKit::WebMouseEvent &)) 0x7febba8c6492 <WebKit::WebPage::mouseEvent(WebKit::WebMouseEvent const&)>) at ../../Source/WebKit/Platform/IPC/HandleMessage.h:47 #21 0x00007febb9f02a2c in IPC::handleMessage<Messages::WebPage::MouseEvent, WebKit::WebPage, void (WebKit::WebPage::*)(WebKit::WebMouseEvent const&)> (decoder=..., object=0x7feb543fa600, function= (void (WebKit::WebPage::*)(WebKit::WebPage * const, const WebKit::WebMouseEvent &)) 0x7febba8c6492 <WebKit::WebPage::mouseEvent(WebKit::WebMouseEvent const&)>) at ../../Source/WebKit/Platform/IPC/HandleMessage.h:133 #22 0x00007febb9efa2c5 in WebKit::WebPage::didReceiveWebPageMessage (this=0x7feb543fa600, connection=..., decoder=...) at DerivedSources/WebKit/WebPageMessageReceiver.cpp:278 #23 0x00007febba8cb582 in WebKit::WebPage::didReceiveMessage (this=0x7feb543fa600, connection=..., decoder=...) at ../../Source/WebKit/WebProcess/WebPage/WebPage.cpp:4258 #24 0x00007febba10a432 in IPC::MessageReceiverMap::dispatchMessage (this=0x8e6e40, connection=..., decoder=...) at ../../Source/WebKit/Platform/IPC/MessageReceiverMap.cpp:123 #25 0x00007febba610068 in WebKit::WebProcess::didReceiveMessage (this=0x8e6dd0, connection=..., decoder=...) at ../../Source/WebKit/WebProcess/WebProcess.cpp:676 #26 0x00007febba0e83b1 in IPC::Connection::dispatchMessage (this=0x7feba24e5000, decoder=...) at ../../Source/WebKit/Platform/IPC/Connection.cpp:978 #27 0x00007febba0e852c in IPC::Connection::dispatchMessage (this=0x7feba24e5000, message=std::unique_ptr<IPC::Decoder> = {...}) at ../../Source/WebKit/Platform/IPC/Connection.cpp:1005 #28 0x00007febba0e8a10 in IPC::Connection::dispatchOneIncomingMessage (this=0x7feba24e5000) at ../../Source/WebKit/Platform/IPC/Connection.cpp:1074 #29 0x00007febba0e80fe in IPC::Connection::<lambda()>::operator()(void) (__closure=0x7feba24fadd8) at ../../Source/WebKit/Platform/IPC/Connection.cpp:956 #30 0x00007febba0efbfa in WTF::Function<void()>::CallableWrapper<IPC::Connection::enqueueIncomingMessage(std::unique_ptr<IPC::Decoder>)::<lambda()> >::call(void) (this=0x7feba24fadd0) at DerivedSources/ForwardingHeaders/wtf/Function.h:101 #31 0x00007febb9f39f42 in WTF::Function<void ()>::operator()() const (this=0x7ffd517691c8) at DerivedSources/ForwardingHeaders/wtf/Function.h:56 #32 0x00007febafa14e67 in WTF::RunLoop::performWork (this=0x7feba24f9000) at ../../Source/WTF/wtf/RunLoop.cpp:106 #33 0x00007febafa60928 in WTF::RunLoop::<lambda(gpointer)>::operator()(gpointer) const (__closure=0x0, userData=0x7feba24f9000) at ../../Source/WTF/wtf/glib/RunLoopGLib.cpp:68 #34 0x00007febafa6094c in WTF::RunLoop::<lambda(gpointer)>::_FUN(gpointer) () at ../../Source/WTF/wtf/glib/RunLoopGLib.cpp:70 #35 0x00007febafa608c8 in WTF::<lambda(GSource*, GSourceFunc, gpointer)>::operator()(GSource *, GSourceFunc, gpointer) const (__closure=0x0, source=0x92a470, callback=0x7febafa6092f <WTF::RunLoop::<lambda(gpointer)>::_FUN(gpointer)>, userData=0x7feba24f9000) at ../../Source/WTF/wtf/glib/RunLoopGLib.cpp:45 #36 0x00007febafa608f8 in WTF::<lambda(GSource*, GSourceFunc, gpointer)>::_FUN(GSource *, GSourceFunc, gpointer) () at ../../Source/WTF/wtf/glib/RunLoopGLib.cpp:46 #37 0x00007feba6eda818 in g_main_dispatch () at /webkit/WebKitBuild/DependenciesGTK/Source/glib-2.54.2/glib/gmain.c:3148 #38 g_main_context_dispatch () at /webkit/WebKitBuild/DependenciesGTK/Source/glib-2.54.2/glib/gmain.c:3813 #39 0x00007feba6edabd8 in g_main_context_iterate () at /webkit/WebKitBuild/DependenciesGTK/Source/glib-2.54.2/glib/gmain.c:3886 #40 0x00007feba6edaec2 in g_main_loop_run () at /webkit/WebKitBuild/DependenciesGTK/Source/glib-2.54.2/glib/gmain.c:4082 #41 0x00007febafa60e06 in WTF::RunLoop::run () at ../../Source/WTF/wtf/glib/RunLoopGLib.cpp:96 #42 0x00007febba93ba71 in WebKit::ChildProcessMain<WebKit::WebProcess, WebKit::WebProcessMain> (argc=3, argv=0x7ffd517695b8) at ../../Source/WebKit/Shared/unix/ChildProcessMain.h:61 #43 0x00007febba93934f in WebKit::WebProcessMainUnix (argc=3, argv=0x7ffd517695b8) at ../../Source/WebKit/WebProcess/gtk/WebProcessMainGtk.cpp:67 #44 0x0000000000400cc1 in main (argc=3, argv=0x7ffd517695b8) at ../../Source/WebKit/WebProcess/EntryPoint/unix/WebProcessMain.cpp:52