The crash is related to formatting, CSS positioning, a VERIFY_NOT_REACHED fail saying // If we get here, ancestor_box was not an ancestor of "box"!. The crash happens at the very beginning of page load. Reduction is below

VERIFICATION FAILED: false at /home/marco/ladybird/Userland/Libraries/LibWeb/Layout/FormattingContext.cpp:1179
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-ak.so.0(ak_verification_failed+0x87) [0x7f745bcd49b7]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0(+0xb2a5c2) [0x7f74602705c2]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_box(Web::Layout::Box const&, Web::Layout::BlockContainer const&, Web::CSSPixels&, Web::Layout::AvailableSpace const&) 0x166) [0x7f746025e426]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_children(Web::Layout::BlockContainer const&, Web::Layout::AvailableSpace const&) 0x94) [0x7f746025f6e4]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::run(Web::Layout::AvailableSpace const&) 0x39) [0x7f746025faa9]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0(+0xb2fa73) [0x7f7460275a73]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::TableFormattingContext::compute_cell_measures() 0x155) [0x7f74602bd305]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::TableFormattingContext::run_until_width_calculation(Web::Layout::AvailableSpace const&) 0x72) [0x7f74602c13a2]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::FormattingContext::compute_table_box_width_inside_table_wrapper(Web::Layout::Box const&, Web::Layout::AvailableSpace const&) 0x27d) [0x7f746027afad]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::compute_width(Web::Layout::Box const&, Web::Layout::AvailableSpace const&) 0x4f4) [0x7f746025bc44]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_box(Web::Layout::Box const&, Web::Layout::BlockContainer const&, Web::CSSPixels&, Web::Layout::AvailableSpace const&) 0x393) [0x7f746025e653]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_children(Web::Layout::BlockContainer const&, Web::Layout::AvailableSpace const&) 0x94) [0x7f746025f6e4]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::run(Web::Layout::AvailableSpace const&) 0x39) [0x7f746025faa9]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::FormattingContext::layout_inside(Web::Layout::Box const&, Web::Layout::LayoutMode, Web::Layout::AvailableSpace const&) 0xdb) [0x7f74602704eb]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_floating_box(Web::Layout::Box const&, Web::Layout::BlockContainer const&, Web::Layout::AvailableSpace const&, Web::CSSPixels, Web::Layout::LineBuilder*) 0xf5) [0x7f746025d485]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_box(Web::Layout::Box const&, Web::Layout::BlockContainer const&, Web::CSSPixels&, Web::Layout::AvailableSpace const&) 0x10a) [0x7f746025e3ca]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_children(Web::Layout::BlockContainer const&, Web::Layout::AvailableSpace const&) 0x94) [0x7f746025f6e4]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_box(Web::Layout::Box const&, Web::Layout::BlockContainer const&, Web::CSSPixels&, Web::Layout::AvailableSpace const&) 0xaec) [0x7f746025edac]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_children(Web::Layout::BlockContainer const&, Web::Layout::AvailableSpace const&) 0x94) [0x7f746025f6e4]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_box(Web::Layout::Box const&, Web::Layout::BlockContainer const&, Web::CSSPixels&, Web::Layout::AvailableSpace const&) 0xaec) [0x7f746025edac]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_children(Web::Layout::BlockContainer const&, Web::Layout::AvailableSpace const&) 0x94) [0x7f746025f6e4]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_box(Web::Layout::Box const&, Web::Layout::BlockContainer const&, Web::CSSPixels&, Web::Layout::AvailableSpace const&) 0xaec) [0x7f746025edac]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_children(Web::Layout::BlockContainer const&, Web::Layout::AvailableSpace const&) 0x94) [0x7f746025f6e4]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::run(Web::Layout::AvailableSpace const&) 0x39) [0x7f746025faa9]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_box(Web::Layout::Box const&, Web::Layout::BlockContainer const&, Web::CSSPixels&, Web::Layout::AvailableSpace const&) 0x5a8) [0x7f746025e868]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Layout::BlockFormattingContext::layout_block_level_children(Web::Layout::BlockContainer const&, Web::Layout::AvailableSpace const&) 0x94) [0x7f746025f6e4]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::DOM::Document::update_layout() 0x23a) [0x7f745ff4fdaa]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::HTML::EventLoop::update_the_rendering() 0x3b4) [0x7f74600959f4]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::HTML::Task::execute() 0x49) [0x7f7460097269]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0(+0x95029d) [0x7f746009629d]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0(+0xc0dc59) [0x7f7460353c59]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-core.so.0 Core::Timer::timer_event(Core::TimerEvent&) 0xb2) [0x7f745e046522]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-core.so.0 Core::EventReceiver::dispatch_event(Core::Event&, Core::EventReceiver*) 0x4d) [0x7f745e0351bd]
/home/marco/ladybird/Build/ladybird/libexec/WebContent(+0x44b9d) [0x55d65c5b1b9d]
/lib/x86_64-linux-gnu/libQt6Core.so.6(+0x183d9b) [0x7f7461db5d9b]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QTimer::timeout(QTimer::QPrivateSignal) 0x3d) [0x7f7461dc0d6d]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QObject::event(QEvent*) 0x1c6) [0x7f7461da8576]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QCoreApplication::notifyInternal2(QObject*, QEvent*) 0xf6) [0x7f7461d6a416]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QTimerInfoList::activateTimers() 0x36b) [0x7f7461ead7ab]
/lib/x86_64-linux-gnu/libQt6Core.so.6(+0x333a29) [0x7f7461f65a29]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(+0x5d5b5) [0x7f745b1d25b5]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(+0xbc717) [0x7f745b231717]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(g_main_context_iteration+0x33) [0x7f745b1d1a53]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) 0x6f) [0x7f7461f635ef]
/home/marco/ladybird/Build/ladybird/libexec/WebContent(+0x44739) [0x55d65c5b1739]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-core.so.0 Core::EventLoop::spin_until(AK::Function<bool ()>) 0xc1) [0x7f745e02d8c1]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::Platform::EventLoopPluginSerenity::spin_until(JS::SafeFunction<bool ()>) 0x11b) [0x7f746035258b]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::HTML::EventLoop::spin_until(JS::SafeFunction<bool ()>) 0x100) [0x7f74600964f0]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::HTML::HTMLParser::handle_text(Web::HTML::HTMLToken&) 0x3e6) [0x7f74601997d6]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::HTML::HTMLParser::run(Web::HTML::HTMLTokenizer::StopAtInsertionPoint) 0x15e) [0x7f746019f9ee]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0 Web::HTML::HTMLParser::run(URL::URL const&, Web::HTML::HTMLTokenizer::StopAtInsertionPoint) 0x136) [0x7f74601a0426]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-web.so.0(+0xc0d2f9) [0x7f74603532f9]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-core.so.0 Core::ThreadEventQueue::process() 0x46a) [0x7f745e04590a]
/home/marco/ladybird/Build/ladybird/libexec/WebContent(+0x44f0d) [0x55d65c5b1f0d]
/home/marco/ladybird/Build/ladybird/libexec/WebContent(+0x48592) [0x55d65c5b5592]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QCoreApplication::notifyInternal2(QObject*, QEvent*) 0xf6) [0x7f7461d6a416]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) 0x1a5) [0x7f7461d6a635]
/lib/x86_64-linux-gnu/libQt6Core.so.6(+0x333a8f) [0x7f7461f65a8f]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(+0x5d5b5) [0x7f745b1d25b5]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(+0xbc717) [0x7f745b231717]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(g_main_context_iteration+0x33) [0x7f745b1d1a53]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) 0x6f) [0x7f7461f635ef]
/lib/x86_64-linux-gnu/libQt6Core.so.6 QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) 0x2e3) [0x7f7461d749a3]
/home/marco/ladybird/Build/ladybird/libexec/../lib/liblagom-core.so.0 Core::EventLoop::exec() 0x4a) [0x7f745e02da3a]
/home/marco/ladybird/Build/ladybird/libexec/WebContent(+0x4aebd) [0x55d65c5b7ebd]
/home/marco/ladybird/Build/ladybird/libexec/WebContent(main+0xf6) [0x55d65c5b1386]
/lib/x86_64-linux-gnu/libc.so.6(+0x2a1ca) [0x7f745b8431ca]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x8b) [0x7f745b84328b]
/home/marco/ladybird/Build/ladybird/libexec/WebContent(+0x444b5) [0x55d65c5b14b5]