I've been working on a menu widget for DevTools but when I tab through the menu items I'm hitting the following assertion once I try to tab past the last item: Assertion failure: owner->GetShadowRoot(), at /home/birtles/src1/dom/base/nsFocusManager.cpp:3440 Call stack when hitting the assertion is as follows: #6 0x00007fb6fc36c576 in nsFocusManager::GetNextTabbableContentInAncestorScopes(nsIContent**, nsIContent*, bool, int*, bool, bool) (this=0x7fb6f8d70900, aStartContent=0x7ffd11081168, aOriginalStartContent= 0x0, aForward=<optimized out>, aCurrentTabIndex=0x7ffd110811e0, aIgnoreTabIndex=<optimized out>, aForDocumentNavigation=<optimized out>) at /home/birtles/src1/dom/base/nsFocusManager.cpp:3440 #7 0x00007fb6fc36a289 in nsFocusManager::GetNextTabbableContent(nsIPresShell*, nsIContent*, nsIContent*, nsIContent*, bool, int, bool, bool, nsIContent**) (this=0x7fb6f8d70900, aPresShell= 0x7fb6c2d88000, aRootContent=0x7fb6c25894c0, aOriginalStartContent=0x0, aStartContent=0x7fb6c25b6f80, aForward=<error reading variable: access outside bounds of object referenced via synthetic pointer>, aCurrentTabIndex=0, aIgnoreTabIndex=<optimized out>, aForDocumentNavigation=<optimized out>, aResultContent=<optimized out>) at /home/birtles/src1/dom/base/nsFocusManager.cpp:3494 #8 0x00007fb6fc36495c in nsFocusManager::DetermineElementToMoveFocus(nsPIDOMWindowOuter*, nsIContent*, int, bool, nsIContent**) (this=<optimized out>, aWindow=0x7fb6c5606c00, aStartContent=<optimized out>, aType=1, aNoParentTraversal=<error reading variable: access outside bounds of object referenced via synthetic pointer>, aNextContent=<optimized out>) at /home/birtles/src1/dom/base/nsFocusManager.cpp:2906 #9 0x00007fb6fc363c93 in nsFocusManager::MoveFocus(mozIDOMWindowProxy*, mozilla::dom::Element*, unsigned int, unsigned int, mozilla::dom::Element**) (this=0x7fb6f8d70900, aWindow=0x7fb6c5606c20, aStartElement= 0x0, aType=<optimized out>, aFlags=8192, aElement=0x7ffd110814b0) at /home/birtles/src1/dom/base/nsFocusManager.cpp:567 #10 0x00007fb6fcf1cc1d in mozilla::EventStateManager::PostHandleKeyboardEvent(mozilla::WidgetKeyboardEvent*, nsIFrame*, nsEventStatus&) (this=<optimized out>, aKeyboardEvent=<optimized out>, aTargetFrame=<optimized out>, aStatus=<optimized out>) at /home/birtles/src1/dom/events/EventStateManager.cpp:3125 #11 0x00007fb6fcf1d1f5 in mozilla::EventStateManager::PostHandleEvent(nsPresContext*, mozilla::WidgetEvent*, nsIFrame*, nsEventStatus*, nsIContent*) (this=<optimized out>, aPresContext= 0x7fb6c3328800, aEvent=0x7ffd11081ce8, aTargetFrame=<optimized out>, aStatus---Type <return> to continue, or q <return> to quit--- =<optimized out>, aOverrideClickTarget=0x0) at /home/birtles/src1/dom/events/EventStateManager.cpp:3767 #12 0x00007fb6fd9a1928 in mozilla::PresShell::HandleEventInternal(mozilla::WidgetEvent*, nsEventStatus*, bool, nsIContent*) (this=<optimized out>, aEvent=0x7ffd11081ce8, aStatus=0x7ffd11081a44, aIsHandlingNativeEvent=<optimized out>, aOverrideClickTarget=0x0) at /home/birtles/src1/layout/base/PresShell.cpp:7660 #13 0x00007fb6fd9a06f7 in mozilla::PresShell::HandleEvent(nsIFrame*, mozilla::WidgetGUIEvent*, bool, nsEventStatus*) (this=<optimized out>, aFrame=<optimized out>, aEvent=<optimized out>, aDontRetargetEvents=<optimized out>, aEventStatus=<optimized out>) at /home/birtles/src1/layout/base/PresShell.cpp:7333 #14 0x00007fb6fd99f95d in mozilla::PresShell::HandleEvent(nsIFrame*, mozilla::WidgetGUIEvent*, bool, nsEventStatus*) (this=<optimized out>, aFrame=<optimized out>, aEvent=<optimized out>, aDontRetargetEvents=<optimized out>, aEventStatus=<optimized out>) at /home/birtles/src1/layout/base/PresShell.cpp:6866 #15 0x00007fb6fd7ad1e0 in nsViewManager::DispatchEvent(mozilla::WidgetGUIEvent*, nsView*, nsEventStatus*) (this=<optimized out>, aEvent=0x7ffd11081ce8, aView=<optimized out>, aStatus=0x7ffd11081a44) at /home/birtles/src1/view/nsViewManager.cpp:812 #16 0x00007fb6fd7acff2 in nsView::HandleEvent(mozilla::WidgetGUIEvent*, bool) (this=<optimized out>, aEvent=0x7ffd11081ce8, aUseAttachedEvents=<optimized out>) at /home/birtles/src1/view/nsView.cpp:1141 #17 0x00007fb6fd7ef91d in nsWindow::DispatchEvent(mozilla::WidgetGUIEvent*, nsEventStatus&) (this=0x7fb6f7f41800, aEvent=0x7ffd11081ce8, aStatus=@0x7ffd11081ad4: nsEventStatus_eIgnore) at /home/birtles/src1/widget/gtk/nsWindow.cpp:578 #18 0x00007fb6fd7b452a in nsBaseWidget::ProcessUntransformedAPZEvent(mozilla::WidgetInputEvent*, mozilla::layers::ScrollableLayerGuid const&, unsigned long, nsEventStatus) (this=0x7fb6f7f41800, aEvent=0x7ffd11081ce8, aGuid=..., aInputBlockId=0, aApzResponse=nsEventStatus_eIgnore) at /home/birtles/src1/widget/nsBaseWidget.cpp:1081 #19 0x00007fb6fd7b4b97 in nsBaseWidget::DispatchInputEvent(mozilla::WidgetInputEvent*) (this=0x7fb6f7f41800, aEvent=0x7ffd11081ce8) at /home/birtles/src1/widget/nsBaseWidget.cpp:1226 #20 0x00007fb6fd7d0a5d in mozilla::widget::TextEventDispatcher::DispatchInputEvent(nsIWidget*, mozilla::WidgetInputEvent&, nsEventStatus&) (this=0x7fb6f1db5120, aWidget=<optimized out>, aEvent= ..., aStatus=@0x7ffd11081ff8: nsEventStatus_eIgnore) at /home/birtles/src1/widget/TextEventDispatcher.cpp:300 #21 0x00007fb6fd7d153a in mozilla::widget::TextEventDispatcher::DispatchKeyboardEventInternal(mozilla::EventMessage, mozilla::WidgetKeyboardEvent const&, nsEventStatus&, void*, unsigned int, bool) (this=0x7fb6f1db5120, aMessage=<optimized out>, aKeyboardEvent=..., aStatus=<optimized out>, aData=<optimized out>, aIndexOfKeypress=0, aNeedsCallback=<optimized out>) at /home/birtles/src1/widget/TextEventDispatcher.cpp:705 #22 0x00007fb6fd7d18b5 in mozilla::widget::TextEventDispatcher::MaybeDispatchKeypressEvents(mozilla::WidgetKeyboardEvent const&, nsEventStatus&, void*, bool) (this=0x7fb70fa07640 <_IO_2_1_stderr_>, aKeyboardEvent=..., aStatus=@0x7ffd11081ff8: nsEventStatus_eIgnore, aData=<optimized out>, aNeedsCallback=<optimized out>)---Type <return> to continue, or q <return> to quit--- at /home/birtles/src1/widget/TextEventDispatcher.cpp:738 #23 0x00007fb6fd7f65eb in nsWindow::OnKeyPressEvent(_GdkEventKey*) (this=0x7fb6f7f41800, aEvent=0x7fb6c56760c0) at /home/birtles/src1/widget/gtk/nsWindow.cpp:3150 This is the rough structure of the content: <window ...> <deck ...> <hbox id="browser" ...> ... <vbox id="appcontent" ...> ... <tabbox id="tabbrowser-tabbox" ...> <tabpanels id="tabbrowser-tabpanels" ...> ... <notificationbox ...> ... <???> [document] <window ...> ... <vbox id="toolbox-container" ...> <div id="toolbox-toolbar-mount" ...> <div class="devtools-tabbar"> ... <div id="toolbox-controls"> <button id="toolbox-meatball-menu-button" ...></button> </div> </div> </div> <tooltip id="aHTMLTooltip" page="true" /> </vbox> <panel consumeoutsideclicks="false" noautofocus="true" ignorekeys="true" tooltip="aHTMLTooltip" type="arrow" level="top" ... panelopen="true"> <html:div class="tooltip-xul-wrapper-inner"> <html:div type="menu" ...> ... <html:div class="tooltip-panel"> <html:div id="toolbox-meatball-menu"> <html:li tabindex="0" id="toolbox-meatball-menu-dock-bottom"> <html:span class="label">Dock to bottom</html:span> </html:li> <html:li tabindex="0" id="toolbox-meatball-menu-dock-right"> <html:span class="label">Dock to right</html:span> </html:li> <html:li tabindex="0" id="toolbox-meatball-menu-dock-left"> <html:span class="label">Dock to left</html:span> </html:li> <html:li tabindex="0" id="toolbox-meatball-menu-dock-window"> <html:span class="label">Separate window</html:span> </html:li> <html:hr /> <html:li tabindex="0" id="toolbox-meatball-menu-splitconsole"> <html:span class="label">Show split console</html:span> <html:span class="accelerator">Esc</html:span> </html:li> <html:li tabindex="0" id="toolbox-meatball-menu-settings"> <html:span class="label">Settings</html:span> <html:span class="accelerator">F1</html:span> </html:li> <html:hr /> <html:li tabindex="0" id="toolbox-meatball-menu-documentation"> <html:span class="label">Documentation…</html:span> </html:li> <html:li tabindex="0" id="toolbox-meatball-menu-community"> <-- Focus is here <html:span class="label">Community…</html:span> </html:li> </html:div> </html:div> </html:div> </html:div> </panel> </window> [/document] </???> </notificationbox> </tabpanels> </tabbox> </vbox> ... </hbox> ... </deck> </window> The code in question from nsFocusManager::GetNextTabbableContentInAncestorScopes is as follows: // If not found in shadow DOM, search from the shadow host in light DOM if (!owner->IsInShadowTree()) { MOZ_ASSERT(owner->GetShadowRoot()); *aStartContent = owner; *aCurrentTabIndex = HostOrSlotTabIndexValue(owner); break; } (Permalink to failing assertion: https://searchfox.org/mozilla-central/rev/f822a0b61631cbb38901569e69b4967176314aa8/dom/base/nsFocusManager.cpp#3440) So presumably owner->IsInShadowTree() is returning false, and owner->GetShadowRoot() is returning nullptr. Olli, I guess this is not expected. Any pointers for where to look?

Does https://bugzilla.mozilla.org/show_bug.cgi?id=1466998 help here? I think it should (or this is something very similar).

(In reply to Olli Pettay [:smaug] from comment #1) > Does https://bugzilla.mozilla.org/show_bug.cgi?id=1466998 help here? I think > it should (or this is something very similar). Yes, that fixes it. Thanks!