###!!! ASSERTION: Compose style for unsupported or non-animatable property, so get invalid RawServoAnimationValues: 'Error', file /home/worker/workspace/build/src/dom/animation/KeyframeEffectReadOnly.cpp, line 551 #01: mozilla::dom::Animation::ComposeStyle [dom/bindings/Nullable.h:60] #02: mozilla::EffectCompositor::GetServoAnimationRule [dom/animation/EffectCompositor.cpp:490] #03: Gecko_GetAnimationRule [layout/style/ServoBindings.cpp:363] #04: style::gecko::wrapper::{{impl}}::get_animation_rules [servo/components/style/gecko/wrapper.rs:344] #05: style::matching::MatchMethods::match_element<style::gecko::wrapper::GeckoElement> [servo/components/style/matching.rs:596] #06: style::traversal::compute_style<style::gecko::wrapper::GeckoElement,style::gecko::traversal::RecalcStyleOnly> [servo/components/style/traversal.rs:498] #07: style::traversal::recalc_style_at<style::gecko::wrapper::GeckoElement,style::gecko::traversal::RecalcStyleOnly> [servo/components/style/traversal.rs:418] #08: style::gecko::traversal::{{impl}}::process_preorder [servo/components/style/gecko/traversal.rs:46] #09: style::sequential::traverse_dom::doit<style::gecko::wrapper::GeckoElement,style::gecko::traversal::RecalcStyleOnly> [servo/components/style/sequential.rs:29] #10: style::traversal::DomTraversal::traverse_children<style::gecko::traversal::RecalcStyleOnly,style::gecko::wrapper::GeckoElement,closure> [servo/components/style/traversal.rs:272] #11: style::sequential::traverse_dom::doit<style::gecko::wrapper::GeckoElement,style::gecko::traversal::RecalcStyleOnly> [servo/components/style/sequential.rs:39] #12: style::traversal::DomTraversal::traverse_children<style::gecko::traversal::RecalcStyleOnly,style::gecko::wrapper::GeckoElement,closure> [servo/components/style/traversal.rs:272] #13: style::sequential::traverse_dom::doit<style::gecko::wrapper::GeckoElement,style::gecko::traversal::RecalcStyleOnly> [servo/components/style/sequential.rs:39] #14: style::sequential::traverse_dom<style::gecko::wrapper::GeckoElement,style::gecko::traversal::RecalcStyleOnly> [servo/components/style/sequential.rs:66] #15: geckoservo::glue::traverse_subtree [servo/ports/geckolib/glue.rs:160] #16: geckoservo::glue::Servo_TraverseSubtree [servo/ports/geckolib/glue.rs:172] #17: mozilla::ServoStyleSet::StyleDocument [layout/style/ServoStyleSet.cpp:544] #18: mozilla::ServoRestyleManager::ProcessPendingRestyles [layout/base/ServoRestyleManager.cpp:330] #19: mozilla::PresShell::FlushPendingNotifications [layout/base/PresShell.cpp:4172] #20: mozilla::PresShell::FlushPendingNotifications [layout/base/PresShell.cpp:4063] #21: nsComputedDOMStyle::GetStyleContextForElement [layout/style/nsComputedDOMStyle.cpp:448] #22: mozilla::dom::KeyframeEffectReadOnly::DoGetTargetStyleContext<(mozilla::dom::KeyframeEffectReadOnly::AnimationStyle)1u> [dom/animation/KeyframeEffectReadOnly.cpp:995] #23: mozilla::dom::KeyframeEffectReadOnly::SetKeyframes [mfbt/AlreadyAddRefed.h:116] #24: mozilla::dom::KeyframeEffectReadOnly::ConstructKeyframeEffect<mozilla::dom::KeyframeEffect, mozilla::dom::UnrestrictedDoubleOrKeyframeAnimationOptions> [dom/animation/KeyframeEffectReadOnly.cpp:831] #25: mozilla::dom::KeyframeEffect::Constructor [dom/animation/KeyframeEffect.cpp:67] #26: mozilla::dom::Element::Animate [dom/base/Element.cpp:3422] #27: mozilla::dom::Element::Animate [mfbt/Maybe.h:439] #28: mozilla::dom::ElementBinding::animate [mfbt/AlreadyAddRefed.h:138] #29: mozilla::dom::GenericBindingMethod [dom/bindings/BindingUtils.cpp:2961] #30: js::CallJSNative [js/src/jscntxtinlines.h:240] #31: js::InternalCallOrConstruct [js/src/vm/Interpreter.cpp:460] #32: Interpret [js/src/vm/Interpreter.cpp:2957] #33: js::RunScript [js/src/vm/Interpreter.cpp:377] #34: js::ExecuteKernel [js/src/vm/Interpreter.cpp:687] #35: js::Execute [js/src/vm/Interpreter.cpp:720] #36: Evaluate [js/src/jsapi.cpp:4503] #37: Evaluate [js/public/RootingAPI.h:795] #38: nsJSUtils::EvaluateString [dom/base/nsJSUtils.cpp:207] #39: nsJSUtils::EvaluateString [dom/base/nsJSUtils.cpp:273] #40: nsScriptLoader::EvaluateScript [js/src/jsapi.h:816] #41: nsScriptLoader::ProcessRequest [dom/base/nsScriptLoader.cpp:1993] #42: nsScriptLoader::ProcessScriptElement [dom/base/nsScriptLoader.cpp:1712] #43: nsScriptElement::MaybeProcessScript [dom/base/nsScriptElement.cpp:148] #44: nsIScriptElement::AttemptToExecute [dom/base/nsIScriptElement.h:223] #45: nsHtml5TreeOpExecutor::RunScript [parser/html/nsHtml5TreeOpExecutor.cpp:682] #46: nsHtml5TreeOpExecutor::RunFlushLoop [dom/base/nsContentSink.h:265] #47: nsHtml5ExecutorFlusher::Run [parser/html/nsHtml5StreamParser.cpp:131] #48: nsThread::ProcessNextEvent [mfbt/Maybe.h:439] #49: NS_ProcessNextEvent [xpcom/threads/nsThreadUtils.cpp:389] #50: mozilla::ipc::MessagePump::Run [ipc/glue/MessagePump.cpp:97] #51: MessageLoop::RunInternal [ipc/chromium/src/base/message_loop.cc:239] #52: MessageLoop::Run [ipc/chromium/src/base/message_loop.cc:502] #53: nsBaseAppShell::Run [widget/nsBaseAppShell.cpp:158] #54: nsAppStartup::Run [toolkit/components/startup/nsAppStartup.cpp:284] #55: XREMain::XRE_mainRun [toolkit/xre/nsAppRunner.cpp:4462] #56: XREMain::XRE_main [toolkit/xre/nsAppRunner.cpp:4638] #57: XRE_main [toolkit/xre/nsAppRunner.cpp:4729] #58: do_main [browser/app/nsBrowserApp.cpp:234] #59: main [browser/app/nsBrowserApp.cpp:307]

This is because transform property is not animatable yet.

Fixed by bug 1332657.