Update:
There have been 32 failures within the last 7 days, all on Linux 18.04 x64 WebRender debug.
Recent failure log: https://treeherder.mozilla.org/logviewer?job_id=380250696&repo=autoland&lineNumber=6785
[task 2022-06-04T22:32:25.040Z] 22:32:25 INFO - TEST-PASS | devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js | The playState of animation [1] should be finished -
[task 2022-06-04T22:32:25.041Z] 22:32:25 INFO - Buffered messages finished
[task 2022-06-04T22:32:25.043Z] 22:32:25 INFO - TEST-UNEXPECTED-FAIL | devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js | The playState of animation [2] should be finished - Got "paused", expected "finished"
[task 2022-06-04T22:32:25.043Z] 22:32:25 INFO - Stack trace:
[task 2022-06-04T22:32:25.043Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:test_is:1422
[task 2022-06-04T22:32:25.043Z] 22:32:25 INFO - chrome://mochitests/content/browser/devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js:assertPlayState/<:53
[task 2022-06-04T22:32:25.043Z] 22:32:25 INFO - chrome://mochitests/content/browser/devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js:assertPlayState:52
[task 2022-06-04T22:32:25.044Z] 22:32:25 INFO - chrome://mochitests/content/browser/devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js:null:26
[task 2022-06-04T22:32:25.044Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:handleTask:989
[task 2022-06-04T22:32:25.044Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:_runTaskBasedTest:1061
[task 2022-06-04T22:32:25.045Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:Tester_execTest:1189
[task 2022-06-04T22:32:25.045Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:nextTest/<:978
[task 2022-06-04T22:32:25.045Z] 22:32:25 INFO - chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:SimpleTest.waitForFocus/<:1041
[task 2022-06-04T22:32:25.046Z] 22:32:25 INFO - Not taking screenshot here: see the one that was previously logged
[task 2022-06-04T22:32:25.073Z] 22:32:25 INFO - TEST-UNEXPECTED-FAIL | devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js | The playState of animation [3] should be finished - Got "paused", expected "finished"
[task 2022-06-04T22:32:25.073Z] 22:32:25 INFO - Stack trace:
[task 2022-06-04T22:32:25.073Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:test_is:1422
[task 2022-06-04T22:32:25.073Z] 22:32:25 INFO - chrome://mochitests/content/browser/devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js:assertPlayState/<:53
[task 2022-06-04T22:32:25.074Z] 22:32:25 INFO - chrome://mochitests/content/browser/devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js:assertPlayState:52
[task 2022-06-04T22:32:25.075Z] 22:32:25 INFO - chrome://mochitests/content/browser/devtools/client/inspector/animation/test/browser_animation_pause-resume-button_end-time.js:null:26
[task 2022-06-04T22:32:25.075Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:handleTask:989
[task 2022-06-04T22:32:25.075Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:_runTaskBasedTest:1061
[task 2022-06-04T22:32:25.075Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:Tester_execTest:1189
[task 2022-06-04T22:32:25.075Z] 22:32:25 INFO - chrome://mochikit/content/browser-test.js:nextTest/<:978
[task 2022-06-04T22:32:25.075Z] 22:32:25 INFO - chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:SimpleTest.waitForFocus/<:1041
[task 2022-06-04T22:32:25.077Z] 22:32:25 INFO - Click 0 on scrubber controller
[task 2022-06-04T22:32:25.080Z] 22:32:25 INFO - GECKO(1616) | [Child 1780: Main Thread]: I/DocShellAndDOMWindowLeak --DOMWINDOW == 1 (7f4235195820) [pid = 1780] [serial = 52] [outer = 0] [url = about:blank]
[task 2022-06-04T22:32:25.081Z] 22:32:25 INFO - Wait until play state will be change to paused
[task 2022-06-04T22:32:25.084Z] 22:32:25 INFO - GECKO(1616) | console.log: "[DISPATCH] action type:" "UPDATE_ANIMATIONS"
[task 2022-06-04T22:32:25.085Z] 22:32:25 INFO - GECKO(1616) | [Child 2936, Main Thread] ###!!! ASSERTION: shouldn't have observed an animation being added twice: 'Error', file /builds/worker/checkouts/gecko/dom/base/nsDOMMutationObserver.h:741
[task 2022-06-04T22:32:25.087Z] 22:32:25 INFO - GECKO(1616) | #01: NS_DebugBreak [xpcom/base/nsDebugImpl.cpp:496]
[task 2022-06-04T22:32:25.088Z] 22:32:25 INFO - GECKO(1616) | #02: nsAnimationReceiver::RecordAnimationMutation(mozilla::dom::Animation*, nsAnimationReceiver::AnimationMutation) [dom/base/nsDOMMutationObserver.cpp:414]
[task 2022-06-04T22:32:25.097Z] 22:32:25 INFO - GECKO(1616) | #03: mozilla::dom::MutationObservers::NotifyAnimationMutated(mozilla::dom::Animation*, mozilla::dom::MutationObservers::AnimationMutationType) [dom/base/MutationObservers.cpp:218]
[task 2022-06-04T22:32:25.099Z] 22:32:25 INFO - GECKO(1616) | #04: mozilla::dom::Animation::UpdateRelevance() [dom/animation/Animation.cpp:1064]
[task 2022-06-04T22:32:25.102Z] 22:32:25 INFO - GECKO(1616) | #05: mozilla::dom::Animation::UpdateEffect(mozilla::PostRestyleMode) [dom/animation/Animation.cpp:1657]
[task 2022-06-04T22:32:25.107Z] 22:32:25 INFO - GECKO(1616) | #06: mozilla::dom::Animation::UpdateTiming(mozilla::dom::Animation::SeekFlag, mozilla::dom::Animation::SyncNotifyFlag) [dom/animation/Animation.cpp:1600]
[task 2022-06-04T22:32:25.108Z] 22:32:25 INFO - GECKO(1616) | #07: mozilla::dom::Animation::SetCurrentTime(mozilla::BaseTimeDuration<mozilla::TimeDurationValueCalculator> const&) [dom/animation/Animation.cpp:366]
[task 2022-06-04T22:32:25.109Z] 22:32:25 INFO - GECKO(1616) | #08: mozilla::dom::Animation::SetCurrentTimeAsDouble(mozilla::dom::Nullable<double> const&, mozilla::ErrorResult&) [dom/animation/Animation.cpp:827]
[task 2022-06-04T22:32:25.111Z] 22:32:25 INFO - GECKO(1616) | #09: mozilla::dom::Animation_Binding::set_currentTime(JSContext*, JS::Handle<JSObject*>, void*, JSJitSetterCallArgs) [s3:gecko-generated-sources:905171b29a79c885e2b7d15d4a366b5fadaa69ecf1446b6b654e69c5b9b81637f281f4b8f3faff66223a885bf47b4345975da3e77cadc47b28cc4d62e91c4a96/dom/bindings/AnimationBinding.cpp::478]
[task 2022-06-04T22:32:25.113Z] 22:32:25 INFO - GECKO(1616) | #10: bool mozilla::dom::binding_detail::GenericSetter<mozilla::dom::binding_detail::NormalThisPolicy>(JSContext*, unsigned int, JS::Value*) [dom/bindings/BindingUtils.cpp:3219]
[task 2022-06-04T22:32:25.114Z] 22:32:25 INFO - GECKO(1616) | #11: CallJSNative(JSContext*, bool (*)(JSContext*, unsigned int, JS::Value*), js::CallReason, JS::CallArgs const&) [js/src/vm/Interpreter.cpp:420]
[task 2022-06-04T22:32:25.115Z] 22:32:25 INFO - GECKO(1616) | #12: js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [js/src/vm/Interpreter.cpp:507]
[task 2022-06-04T22:32:25.116Z] 22:32:25 INFO - GECKO(1616) | #13: js::Call(JSContext*, JS::Handle<JS::Value>, JS::Handle<JS::Value>, js::AnyInvokeArgs const&, JS::MutableHandle<JS::Value>, js::CallReason) [js/src/vm/Interpreter.cpp:605]
[task 2022-06-04T22:32:25.116Z] 22:32:25 INFO - GECKO(1616) | #14: js::CallSetter(JSContext*, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::Handle<JS::Value>) [js/src/vm/Interpreter.cpp:747]
[task 2022-06-04T22:32:25.118Z] 22:32:25 INFO - GECKO(1616) | #15: js::SetPropertyIgnoringNamedGetter(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::Handle<mozilla::Maybe<JS::PropertyDescriptor> >, JS::ObjectOpResult&) [js/src/proxy/BaseProxyHandler.cpp:239]
[task 2022-06-04T22:32:25.120Z] 22:32:25 INFO - GECKO(1616) | #16: js::BaseProxyHandler::set(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) const [js/src/proxy/BaseProxyHandler.cpp:155]
[task 2022-06-04T22:32:25.121Z] 22:32:25 INFO - GECKO(1616) | #17: js::Proxy::setInternal(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) [js/src/proxy/Proxy.cpp:539]
[task 2022-06-04T22:32:25.122Z] 22:32:25 INFO - GECKO(1616) | #18: js::Proxy::set(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) [js/src/proxy/Proxy.cpp:551]
[task 2022-06-04T22:32:25.123Z] 22:32:25 INFO - GECKO(1616) | #19: js::SetPropertyIgnoringNamedGetter(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::Handle<mozilla::Maybe<JS::PropertyDescriptor> >, JS::ObjectOpResult&) [js/src/proxy/BaseProxyHandler.cpp:174]
[task 2022-06-04T22:32:25.124Z] 22:32:25 INFO - GECKO(1616) | #20: js::BaseProxyHandler::set(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) const [js/src/proxy/BaseProxyHandler.cpp:155]
[task 2022-06-04T22:32:25.125Z] 22:32:25 INFO - GECKO(1616) | #21: js::Proxy::setInternal(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) [js/src/proxy/Proxy.cpp:539]
[task 2022-06-04T22:32:25.126Z] 22:32:25 INFO - GECKO(1616) | #22: js::Proxy::set(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) [js/src/proxy/Proxy.cpp:551]
[task 2022-06-04T22:32:25.134Z] 22:32:25 INFO - GECKO(1616) | #23: js::SetPropertyIgnoringNamedGetter(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::Handle<mozilla::Maybe<JS::PropertyDescriptor> >, JS::ObjectOpResult&) [js/src/proxy/BaseProxyHandler.cpp:174]
[task 2022-06-04T22:32:25.137Z] 22:32:25 INFO - GECKO(1616) | #24: js::BaseProxyHandler::set(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) const [js/src/proxy/BaseProxyHandler.cpp:155]
[task 2022-06-04T22:32:25.139Z] 22:32:25 INFO - GECKO(1616) | #25: js::Proxy::setInternal(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) [js/src/proxy/Proxy.cpp:539]
[task 2022-06-04T22:32:25.140Z] 22:32:25 INFO - GECKO(1616) | #26: js::Proxy::set(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::ObjectOpResult&) [js/src/proxy/Proxy.cpp:551]
[task 2022-06-04T22:32:25.142Z] 22:32:25 INFO - GECKO(1616) | #27: SetObjectElementOperation(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::PropertyKey>, JS::Handle<JS::Value>, JS::Handle<JS::Value>, bool) [js/src/vm/Interpreter.cpp:1817]
[task 2022-06-04T22:32:25.143Z] 22:32:25 INFO - GECKO(1616) | #28: Interpret(JSContext*, js::RunState&) [js/src/vm/Interpreter.cpp:3075]
[task 2022-06-04T22:32:25.144Z] 22:32:25 INFO - GECKO(1616) | #29: js::RunScript(JSContext*, js::RunState&) [js/src/vm/Interpreter.cpp:389]
[task 2022-06-04T22:32:25.149Z] 22:32:25 INFO - GECKO(1616) | #30: js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [js/src/vm/Interpreter.cpp:539]
[task 2022-06-04T22:32:25.156Z] 22:32:25 INFO - GECKO(1616) | #31: js::Call(JSContext*, JS::Handle<JS::Value>, JS::Handle<JS::Value>, js::AnyInvokeArgs const&, JS::MutableHandle<JS::Value>, js::CallReason) [js/src/vm/Interpreter.cpp:605]
[task 2022-06-04T22:32:25.160Z] 22:32:25 INFO - GECKO(1616) | #32: js::fun_apply(JSContext*, unsigned int, JS::Value*) [js/src/vm/JSFunction.cpp:1023]
[task 2022-06-04T22:32:25.162Z] 22:32:25 INFO - GECKO(1616) | #33: CallJSNative(JSContext*, bool (*)(JSContext*, unsigned int, JS::Value*), js::CallReason, JS::CallArgs const&) [js/src/vm/Interpreter.cpp:420]
[task 2022-06-04T22:32:25.162Z] 22:32:25 INFO - GECKO(1616) | #34: js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [js/src/vm/Interpreter.cpp:507]
[task 2022-06-04T22:32:25.163Z] 22:32:25 INFO - GECKO(1616) | #35: js::jit::DoCallFallback(JSContext*, js::jit::BaselineFrame*, js::jit::ICFallbackStub*, unsigned int, JS::Value*, JS::MutableHandle<JS::Value>) [js/src/jit/BaselineIC.cpp:1582]
[task 2022-06-04T22:32:25.164Z] 22:32:25 INFO - GECKO(1616) | #36: ??? (???:???)
[task 2022-06-04T22:32:25.165Z] 22:32:25 INFO - GECKO(1616) | [Child 2936, Main Thread] ###!!! ASSERTION: shouldn't have observed an animation being added twice: 'Error', file /builds/worker/checkouts/gecko/dom/base/nsDOMMutationObserver.h:741
[task 2022-06-04T22:32:25.165Z] 22:32:25 INFO - GECKO(1616) | #01: NS_DebugBreak [xpcom/base/nsDebugImpl.cpp:496]
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