From 6bf0a5cb5034a7e684dcc3500e841785237ce2dd Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 19:32:43 +0200
Subject: Adding upstream version 1:115.7.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 dom/animation/test/chrome.ini                      |   29 +
 dom/animation/test/chrome/file_animate_xrays.html  |   18 +
 dom/animation/test/chrome/test_animate_xrays.html  |   40 +
 .../chrome/test_animation_observers_async.html     |  665 ++++++
 .../test/chrome/test_animation_observers_sync.html | 1587 ++++++++++++++
 .../chrome/test_animation_performance_warning.html | 1692 +++++++++++++++
 .../test/chrome/test_animation_properties.html     |  838 +++++++
 .../chrome/test_animation_properties_display.html  |   43 +
 .../test_cssanimation_missing_keyframes.html       |   73 +
 .../test_generated_content_getAnimations.html      |   83 +
 .../test/chrome/test_keyframe_effect_xrays.html    |   45 +
 ...bserver_for_element_removal_in_shadow_tree.html |   45 +
 .../test/chrome/test_running_on_compositor.html    | 1516 +++++++++++++
 .../test_simulate_compute_values_failure.html      |  371 ++++
 dom/animation/test/crashtests/1134538.html         |    8 +
 dom/animation/test/crashtests/1216842-1.html       |   35 +
 dom/animation/test/crashtests/1216842-2.html       |   35 +
 dom/animation/test/crashtests/1216842-3.html       |   27 +
 dom/animation/test/crashtests/1216842-4.html       |   27 +
 dom/animation/test/crashtests/1216842-5.html       |   38 +
 dom/animation/test/crashtests/1216842-6.html       |   38 +
 dom/animation/test/crashtests/1239889-1.html       |   16 +
 dom/animation/test/crashtests/1244595-1.html       |    3 +
 dom/animation/test/crashtests/1272475-1.html       |   20 +
 dom/animation/test/crashtests/1272475-2.html       |   20 +
 dom/animation/test/crashtests/1277272-1-inner.html |   19 +
 dom/animation/test/crashtests/1277272-1.html       |   25 +
 dom/animation/test/crashtests/1278485-1.html       |   26 +
 dom/animation/test/crashtests/1282691-1.html       |   23 +
 dom/animation/test/crashtests/1291413-1.html       |   20 +
 dom/animation/test/crashtests/1291413-2.html       |   21 +
 dom/animation/test/crashtests/1304886-1.html       |   14 +
 dom/animation/test/crashtests/1309198-1.html       |   40 +
 dom/animation/test/crashtests/1322291-1.html       |   24 +
 dom/animation/test/crashtests/1322291-2.html       |   31 +
 dom/animation/test/crashtests/1322382-1.html       |   16 +
 dom/animation/test/crashtests/1323114-1.html       |   12 +
 dom/animation/test/crashtests/1323114-2.html       |   18 +
 dom/animation/test/crashtests/1323119-1.html       |   13 +
 dom/animation/test/crashtests/1324554-1.html       |   19 +
 dom/animation/test/crashtests/1325193-1.html       |   18 +
 dom/animation/test/crashtests/1330190-1.html       |   11 +
 dom/animation/test/crashtests/1330190-2.html       |   36 +
 dom/animation/test/crashtests/1330513-1.html       |    8 +
 dom/animation/test/crashtests/1332588-1.html       |   25 +
 dom/animation/test/crashtests/1333539-1.html       |   30 +
 dom/animation/test/crashtests/1333539-2.html       |   38 +
 dom/animation/test/crashtests/1334582-1.html       |   11 +
 dom/animation/test/crashtests/1334582-2.html       |   11 +
 dom/animation/test/crashtests/1334583-1.html       |    9 +
 dom/animation/test/crashtests/1335998-1.html       |   28 +
 dom/animation/test/crashtests/1343589-1.html       |   18 +
 dom/animation/test/crashtests/1359658-1.html       |   33 +
 dom/animation/test/crashtests/1373712-1.html       |   11 +
 dom/animation/test/crashtests/1379606-1.html       |   21 +
 dom/animation/test/crashtests/1393605-1.html       |   15 +
 dom/animation/test/crashtests/1400022-1.html       |   10 +
 dom/animation/test/crashtests/1401809.html         |   14 +
 dom/animation/test/crashtests/1411318-1.html       |   15 +
 dom/animation/test/crashtests/1467277-1.html       |    6 +
 dom/animation/test/crashtests/1468294-1.html       |    7 +
 dom/animation/test/crashtests/1524480-1.html       |   37 +
 dom/animation/test/crashtests/1575926.html         |   24 +
 dom/animation/test/crashtests/1585770.html         |   22 +
 dom/animation/test/crashtests/1604500-1.html       |   24 +
 dom/animation/test/crashtests/1611847.html         |   23 +
 dom/animation/test/crashtests/1612891-1.html       |   15 +
 dom/animation/test/crashtests/1612891-2.html       |   15 +
 dom/animation/test/crashtests/1612891-3.html       |   10 +
 dom/animation/test/crashtests/1633442.html         |   15 +
 dom/animation/test/crashtests/1633486.html         |   20 +
 dom/animation/test/crashtests/1656419.html         |   23 +
 dom/animation/test/crashtests/1699890.html         |   13 +
 dom/animation/test/crashtests/1706157.html         |   19 +
 dom/animation/test/crashtests/1714421.html         |    8 +
 dom/animation/test/crashtests/1807966.html         |   13 +
 dom/animation/test/crashtests/crashtests.list      |   61 +
 .../document-timeline/test_document-timeline.html  |  147 ++
 .../test_request_animation_frame.html              |   27 +
 dom/animation/test/mochitest.ini                   |   81 +
 dom/animation/test/mozilla/empty.html              |    2 +
 .../test/mozilla/file_deferred_start.html          |  179 ++
 .../file_disable_animations_api_autoremove.html    |   69 +
 .../file_disable_animations_api_compositing.html   |  137 ++
 ...file_disable_animations_api_get_animations.html |   20 +
 ..._disable_animations_api_implicit_keyframes.html |   48 +
 .../file_disable_animations_api_timelines.html     |   30 +
 .../test/mozilla/file_discrete_animations.html     |  122 ++
 dom/animation/test/mozilla/file_restyles.html      | 2275 ++++++++++++++++++++
 .../file_transition_finish_on_compositor.html      |   67 +
 dom/animation/test/mozilla/test_cascade.html       |   37 +
 .../test/mozilla/test_cubic_bezier_limits.html     |  168 ++
 .../test/mozilla/test_deferred_start.html          |   21 +
 .../test_disable_animations_api_autoremove.html    |   15 +
 .../test_disable_animations_api_compositing.html   |   14 +
 ...test_disable_animations_api_get_animations.html |   14 +
 ..._disable_animations_api_implicit_keyframes.html |   14 +
 .../test_disable_animations_api_timelines.html     |   16 +
 .../test/mozilla/test_disabled_properties.html     |   73 +
 .../test/mozilla/test_discrete_animations.html     |   16 +
 .../test/mozilla/test_distance_of_basic_shape.html |   91 +
 .../test/mozilla/test_distance_of_filter.html      |  248 +++
 .../mozilla/test_distance_of_path_function.html    |  140 ++
 .../test/mozilla/test_distance_of_transform.html   |  404 ++++
 .../test_document_timeline_origin_time_range.html  |   32 +
 .../test/mozilla/test_event_listener_leaks.html    |   43 +
 .../test_get_animations_on_scroll_animations.html  |   74 +
 dom/animation/test/mozilla/test_hide_and_show.html |  198 ++
 .../test_mainthread_synchronization_pref.html      |   42 +
 .../test/mozilla/test_moz_prefixed_properties.html |   93 +
 .../mozilla/test_pending_animation_tracker.html    |  134 ++
 dom/animation/test/mozilla/test_restyles.html      |   22 +
 .../test/mozilla/test_restyling_xhr_doc.html       |  106 +
 dom/animation/test/mozilla/test_set_easing.html    |   36 +
 .../test_style_after_finished_on_compositor.html   |  138 ++
 .../test/mozilla/test_transform_limits.html        |   56 +
 .../test_transition_finish_on_compositor.html      |   22 +
 .../mozilla/test_underlying_discrete_value.html    |  188 ++
 dom/animation/test/mozilla/test_unstyled.html      |   54 +
 dom/animation/test/mozilla/xhr_doc.html            |    2 +
 .../test_animation-seeking-with-current-time.html  |  123 ++
 .../test_animation-seeking-with-start-time.html    |  123 ++
 .../test/style/test_animation-setting-effect.html  |  127 ++
 dom/animation/test/style/test_composite.html       |  142 ++
 ...terpolation-from-interpolatematrix-to-none.html |   43 +
 .../style/test_missing-keyframe-on-compositor.html |  577 +++++
 .../test/style/test_missing-keyframe.html          |  110 +
 .../test_transform-non-normalizable-rotate3d.html  |   28 +
 dom/animation/test/testcommon.js                   |  527 +++++
 129 files changed, 15865 insertions(+)
 create mode 100644 dom/animation/test/chrome.ini
 create mode 100644 dom/animation/test/chrome/file_animate_xrays.html
 create mode 100644 dom/animation/test/chrome/test_animate_xrays.html
 create mode 100644 dom/animation/test/chrome/test_animation_observers_async.html
 create mode 100644 dom/animation/test/chrome/test_animation_observers_sync.html
 create mode 100644 dom/animation/test/chrome/test_animation_performance_warning.html
 create mode 100644 dom/animation/test/chrome/test_animation_properties.html
 create mode 100644 dom/animation/test/chrome/test_animation_properties_display.html
 create mode 100644 dom/animation/test/chrome/test_cssanimation_missing_keyframes.html
 create mode 100644 dom/animation/test/chrome/test_generated_content_getAnimations.html
 create mode 100644 dom/animation/test/chrome/test_keyframe_effect_xrays.html
 create mode 100644 dom/animation/test/chrome/test_mutation_observer_for_element_removal_in_shadow_tree.html
 create mode 100644 dom/animation/test/chrome/test_running_on_compositor.html
 create mode 100644 dom/animation/test/chrome/test_simulate_compute_values_failure.html
 create mode 100644 dom/animation/test/crashtests/1134538.html
 create mode 100644 dom/animation/test/crashtests/1216842-1.html
 create mode 100644 dom/animation/test/crashtests/1216842-2.html
 create mode 100644 dom/animation/test/crashtests/1216842-3.html
 create mode 100644 dom/animation/test/crashtests/1216842-4.html
 create mode 100644 dom/animation/test/crashtests/1216842-5.html
 create mode 100644 dom/animation/test/crashtests/1216842-6.html
 create mode 100644 dom/animation/test/crashtests/1239889-1.html
 create mode 100644 dom/animation/test/crashtests/1244595-1.html
 create mode 100644 dom/animation/test/crashtests/1272475-1.html
 create mode 100644 dom/animation/test/crashtests/1272475-2.html
 create mode 100644 dom/animation/test/crashtests/1277272-1-inner.html
 create mode 100644 dom/animation/test/crashtests/1277272-1.html
 create mode 100644 dom/animation/test/crashtests/1278485-1.html
 create mode 100644 dom/animation/test/crashtests/1282691-1.html
 create mode 100644 dom/animation/test/crashtests/1291413-1.html
 create mode 100644 dom/animation/test/crashtests/1291413-2.html
 create mode 100644 dom/animation/test/crashtests/1304886-1.html
 create mode 100644 dom/animation/test/crashtests/1309198-1.html
 create mode 100644 dom/animation/test/crashtests/1322291-1.html
 create mode 100644 dom/animation/test/crashtests/1322291-2.html
 create mode 100644 dom/animation/test/crashtests/1322382-1.html
 create mode 100644 dom/animation/test/crashtests/1323114-1.html
 create mode 100644 dom/animation/test/crashtests/1323114-2.html
 create mode 100644 dom/animation/test/crashtests/1323119-1.html
 create mode 100644 dom/animation/test/crashtests/1324554-1.html
 create mode 100644 dom/animation/test/crashtests/1325193-1.html
 create mode 100644 dom/animation/test/crashtests/1330190-1.html
 create mode 100644 dom/animation/test/crashtests/1330190-2.html
 create mode 100644 dom/animation/test/crashtests/1330513-1.html
 create mode 100644 dom/animation/test/crashtests/1332588-1.html
 create mode 100644 dom/animation/test/crashtests/1333539-1.html
 create mode 100644 dom/animation/test/crashtests/1333539-2.html
 create mode 100644 dom/animation/test/crashtests/1334582-1.html
 create mode 100644 dom/animation/test/crashtests/1334582-2.html
 create mode 100644 dom/animation/test/crashtests/1334583-1.html
 create mode 100644 dom/animation/test/crashtests/1335998-1.html
 create mode 100644 dom/animation/test/crashtests/1343589-1.html
 create mode 100644 dom/animation/test/crashtests/1359658-1.html
 create mode 100644 dom/animation/test/crashtests/1373712-1.html
 create mode 100644 dom/animation/test/crashtests/1379606-1.html
 create mode 100644 dom/animation/test/crashtests/1393605-1.html
 create mode 100644 dom/animation/test/crashtests/1400022-1.html
 create mode 100644 dom/animation/test/crashtests/1401809.html
 create mode 100644 dom/animation/test/crashtests/1411318-1.html
 create mode 100644 dom/animation/test/crashtests/1467277-1.html
 create mode 100644 dom/animation/test/crashtests/1468294-1.html
 create mode 100644 dom/animation/test/crashtests/1524480-1.html
 create mode 100644 dom/animation/test/crashtests/1575926.html
 create mode 100644 dom/animation/test/crashtests/1585770.html
 create mode 100644 dom/animation/test/crashtests/1604500-1.html
 create mode 100644 dom/animation/test/crashtests/1611847.html
 create mode 100644 dom/animation/test/crashtests/1612891-1.html
 create mode 100644 dom/animation/test/crashtests/1612891-2.html
 create mode 100644 dom/animation/test/crashtests/1612891-3.html
 create mode 100644 dom/animation/test/crashtests/1633442.html
 create mode 100644 dom/animation/test/crashtests/1633486.html
 create mode 100644 dom/animation/test/crashtests/1656419.html
 create mode 100644 dom/animation/test/crashtests/1699890.html
 create mode 100644 dom/animation/test/crashtests/1706157.html
 create mode 100644 dom/animation/test/crashtests/1714421.html
 create mode 100644 dom/animation/test/crashtests/1807966.html
 create mode 100644 dom/animation/test/crashtests/crashtests.list
 create mode 100644 dom/animation/test/document-timeline/test_document-timeline.html
 create mode 100644 dom/animation/test/document-timeline/test_request_animation_frame.html
 create mode 100644 dom/animation/test/mochitest.ini
 create mode 100644 dom/animation/test/mozilla/empty.html
 create mode 100644 dom/animation/test/mozilla/file_deferred_start.html
 create mode 100644 dom/animation/test/mozilla/file_disable_animations_api_autoremove.html
 create mode 100644 dom/animation/test/mozilla/file_disable_animations_api_compositing.html
 create mode 100644 dom/animation/test/mozilla/file_disable_animations_api_get_animations.html
 create mode 100644 dom/animation/test/mozilla/file_disable_animations_api_implicit_keyframes.html
 create mode 100644 dom/animation/test/mozilla/file_disable_animations_api_timelines.html
 create mode 100644 dom/animation/test/mozilla/file_discrete_animations.html
 create mode 100644 dom/animation/test/mozilla/file_restyles.html
 create mode 100644 dom/animation/test/mozilla/file_transition_finish_on_compositor.html
 create mode 100644 dom/animation/test/mozilla/test_cascade.html
 create mode 100644 dom/animation/test/mozilla/test_cubic_bezier_limits.html
 create mode 100644 dom/animation/test/mozilla/test_deferred_start.html
 create mode 100644 dom/animation/test/mozilla/test_disable_animations_api_autoremove.html
 create mode 100644 dom/animation/test/mozilla/test_disable_animations_api_compositing.html
 create mode 100644 dom/animation/test/mozilla/test_disable_animations_api_get_animations.html
 create mode 100644 dom/animation/test/mozilla/test_disable_animations_api_implicit_keyframes.html
 create mode 100644 dom/animation/test/mozilla/test_disable_animations_api_timelines.html
 create mode 100644 dom/animation/test/mozilla/test_disabled_properties.html
 create mode 100644 dom/animation/test/mozilla/test_discrete_animations.html
 create mode 100644 dom/animation/test/mozilla/test_distance_of_basic_shape.html
 create mode 100644 dom/animation/test/mozilla/test_distance_of_filter.html
 create mode 100644 dom/animation/test/mozilla/test_distance_of_path_function.html
 create mode 100644 dom/animation/test/mozilla/test_distance_of_transform.html
 create mode 100644 dom/animation/test/mozilla/test_document_timeline_origin_time_range.html
 create mode 100644 dom/animation/test/mozilla/test_event_listener_leaks.html
 create mode 100644 dom/animation/test/mozilla/test_get_animations_on_scroll_animations.html
 create mode 100644 dom/animation/test/mozilla/test_hide_and_show.html
 create mode 100644 dom/animation/test/mozilla/test_mainthread_synchronization_pref.html
 create mode 100644 dom/animation/test/mozilla/test_moz_prefixed_properties.html
 create mode 100644 dom/animation/test/mozilla/test_pending_animation_tracker.html
 create mode 100644 dom/animation/test/mozilla/test_restyles.html
 create mode 100644 dom/animation/test/mozilla/test_restyling_xhr_doc.html
 create mode 100644 dom/animation/test/mozilla/test_set_easing.html
 create mode 100644 dom/animation/test/mozilla/test_style_after_finished_on_compositor.html
 create mode 100644 dom/animation/test/mozilla/test_transform_limits.html
 create mode 100644 dom/animation/test/mozilla/test_transition_finish_on_compositor.html
 create mode 100644 dom/animation/test/mozilla/test_underlying_discrete_value.html
 create mode 100644 dom/animation/test/mozilla/test_unstyled.html
 create mode 100644 dom/animation/test/mozilla/xhr_doc.html
 create mode 100644 dom/animation/test/style/test_animation-seeking-with-current-time.html
 create mode 100644 dom/animation/test/style/test_animation-seeking-with-start-time.html
 create mode 100644 dom/animation/test/style/test_animation-setting-effect.html
 create mode 100644 dom/animation/test/style/test_composite.html
 create mode 100644 dom/animation/test/style/test_interpolation-from-interpolatematrix-to-none.html
 create mode 100644 dom/animation/test/style/test_missing-keyframe-on-compositor.html
 create mode 100644 dom/animation/test/style/test_missing-keyframe.html
 create mode 100644 dom/animation/test/style/test_transform-non-normalizable-rotate3d.html
 create mode 100644 dom/animation/test/testcommon.js

(limited to 'dom/animation/test')

diff --git a/dom/animation/test/chrome.ini b/dom/animation/test/chrome.ini
new file mode 100644
index 0000000000..4001899a50
--- /dev/null
+++ b/dom/animation/test/chrome.ini
@@ -0,0 +1,29 @@
+[DEFAULT]
+prefs =
+  dom.animations-api.autoremove.enabled=true
+  dom.animations-api.compositing.enabled=true
+  dom.animations.mainthread-synchronization-with-geometric-animations=true
+  gfx.omta.background-color=true
+  layout.css.individual-transform.enabled=true
+  layout.css.motion-path.enabled=true
+support-files =
+  testcommon.js
+  ../../imptests/testharness.js
+  ../../imptests/testharnessreport.js
+  !/dom/animation/test/chrome/file_animate_xrays.html
+
+[chrome/test_animate_xrays.html]
+# file_animate_xrays.html needs to go in mochitest.ini since it is served
+# over HTTP
+[chrome/test_keyframe_effect_xrays.html]
+[chrome/test_animation_observers_async.html]
+[chrome/test_animation_observers_sync.html]
+[chrome/test_animation_performance_warning.html]
+[chrome/test_animation_properties.html]
+[chrome/test_animation_properties_display.html]
+[chrome/test_cssanimation_missing_keyframes.html]
+[chrome/test_generated_content_getAnimations.html]
+[chrome/test_mutation_observer_for_element_removal_in_shadow_tree.html]
+[chrome/test_running_on_compositor.html]
+[chrome/test_simulate_compute_values_failure.html]
+skip-if = !debug
diff --git a/dom/animation/test/chrome/file_animate_xrays.html b/dom/animation/test/chrome/file_animate_xrays.html
new file mode 100644
index 0000000000..2fa15b1764
--- /dev/null
+++ b/dom/animation/test/chrome/file_animate_xrays.html
@@ -0,0 +1,18 @@
+<!doctype html>
+<html>
+<head>
+<meta charset=utf-8>
+<script>
+Element.prototype.animate = function() {
+  throw 'Called animate() as defined in content document';
+}
+for (let name of ["KeyframeEffect", "Animation"]) {
+  this[name] = function() {
+    throw `Called overridden ${name} constructor`;
+  };
+}
+</script>
+<body>
+<div id="target"></div>
+</body>
+</html>
diff --git a/dom/animation/test/chrome/test_animate_xrays.html b/dom/animation/test/chrome/test_animate_xrays.html
new file mode 100644
index 0000000000..64df6db720
--- /dev/null
+++ b/dom/animation/test/chrome/test_animate_xrays.html
@@ -0,0 +1,40 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+</head>
+<body>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1414674"
+  target="_blank">Mozilla Bug 1414674</a>
+<div id="log"></div>
+<iframe id="iframe"
+  src="http://example.org/tests/dom/animation/test/chrome/file_animate_xrays.html"></iframe>
+<script>
+'use strict';
+
+var win = document.getElementById('iframe').contentWindow;
+
+async_test(function(t) {
+  window.addEventListener('load', t.step_func(function() {
+    var target = win.document.getElementById('target');
+    var anim = target.animate({opacity: [ 1, 0 ]}, 100 * MS_PER_SEC);
+    // The frames object should be accessible via x-ray.
+    var frames = anim.effect.getKeyframes();
+    assert_equals(frames.length, 2,
+                  "frames for Element.animate should be non-zero");
+    assert_equals(frames[0].opacity, "1",
+                  "first frame opacity for Element.animate should be specified value");
+    assert_equals(frames[0].computedOffset, 0,
+                  "first frame offset for Element.animate should be 0");
+    assert_equals(frames[1].opacity, "0",
+                  "last frame opacity for Element.animate should be specified value");
+    assert_equals(frames[1].computedOffset, 1,
+                  "last frame offset for Element.animate should be 1");
+    t.done();
+  }));
+}, 'Calling animate() across x-rays');
+
+</script>
+</body>
diff --git a/dom/animation/test/chrome/test_animation_observers_async.html b/dom/animation/test/chrome/test_animation_observers_async.html
new file mode 100644
index 0000000000..7505baca53
--- /dev/null
+++ b/dom/animation/test/chrome/test_animation_observers_async.html
@@ -0,0 +1,665 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>
+Test chrome-only MutationObserver animation notifications (async tests)
+</title>
+<!--
+
+  This file contains tests for animation mutation observers that require
+  some asynchronous steps (e.g. waiting for animation events).
+
+  Where possible, however, we prefer to write synchronous tests since they are
+  less to timeout when run on automation. These synchronous tests are located
+  in test_animation_observers_sync.html.
+
+-->
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<div id="log"></div>
+<style>
+@keyframes anim {
+  to { transform: translate(100px); }
+}
+@keyframes anotherAnim {
+  to { transform: translate(0px); }
+}
+#target {
+  width: 100px;
+  height: 100px;
+  background-color: yellow;
+  line-height: 16px;
+}
+</style>
+<div id=container><div id=target></div></div>
+<script>
+var div = document.getElementById("target");
+var gRecords = [];
+var gObserver = new MutationObserver(newRecords => {
+  gRecords.push(...newRecords);
+});
+
+function setupAsynchronousObserver(t, options) {
+
+  gRecords = [];
+  t.add_cleanup(() => {
+    gObserver.disconnect();
+  });
+  gObserver.observe(options.subtree ? div.parentNode : div,
+                    { animations: true, subtree: options.subtree });
+}
+
+// Adds an event listener and returns a Promise that is resolved when the
+// event listener is called.
+function await_event(aElement, aEventName) {
+  return new Promise(aResolve => {
+    function listener(aEvent) {
+      aElement.removeEventListener(aEventName, listener);
+      aResolve();
+    }
+    aElement.addEventListener(aEventName, listener);
+  });
+}
+
+function assert_record_list(actual, expected, desc, index, listName) {
+  assert_equals(actual.length, expected.length,
+    `${desc} - record[${index}].${listName} length`);
+  if (actual.length != expected.length) {
+    return;
+  }
+  for (var i = 0; i < actual.length; i++) {
+    assert_not_equals(actual.indexOf(expected[i]), -1,
+      `${desc} - record[${index}].${listName} contains expected Animation`);
+  }
+}
+
+function assert_records(expected, desc) {
+  var records = gRecords;
+  gRecords = [];
+  assert_equals(records.length, expected.length, `${desc} - number of records`);
+  if (records.length != expected.length) {
+    return;
+  }
+  for (var i = 0; i < records.length; i++) {
+    assert_record_list(records[i].addedAnimations, expected[i].added, desc, i, "addedAnimations");
+    assert_record_list(records[i].changedAnimations, expected[i].changed, desc, i, "changedAnimations");
+    assert_record_list(records[i].removedAnimations, expected[i].removed, desc, i, "removedAnimations");
+  }
+}
+
+function assert_records_any_order(expected, desc) {
+  // Generate a unique label for each Animation object.
+  let animation_labels = new Map();
+  let animation_counter = 0;
+  for (let record of gRecords) {
+    for (let a of [...record.addedAnimations, ...record.changedAnimations, ...record.removedAnimations]) {
+      if (!animation_labels.has(a)) {
+        animation_labels.set(a, ++animation_counter);
+      }
+    }
+  }
+  for (let record of expected) {
+    for (let a of [...record.added, ...record.changed, ...record.removed]) {
+      if (!animation_labels.has(a)) {
+        animation_labels.set(a, ++animation_counter);
+      }
+    }
+  }
+
+  function record_label(record) {
+    // Generate a label of the form:
+    //
+    //   <added-animations>:<changed-animations>:<removed-animations>
+    let added   = record.addedAnimations   || record.added;
+    let changed = record.changedAnimations || record.changed;
+    let removed = record.removedAnimations || record.removed;
+    return [added  .map(a => animation_labels.get(a)).sort().join(),
+            changed.map(a => animation_labels.get(a)).sort().join(),
+            removed.map(a => animation_labels.get(a)).sort().join()]
+           .join(":");
+  }
+
+  // Sort records by their label.
+  gRecords.sort((a, b) => record_label(a) < record_label(b));
+  expected.sort((a, b) => record_label(a) < record_label(b));
+
+  // Assert the sorted record lists are equal.
+  assert_records(expected, desc);
+}
+
+// -- Tests ------------------------------------------------------------------
+
+// We run all tests first targeting the div and observing the div, then again
+// targeting the div and observing its parent while using the subtree:true
+// MutationObserver option.
+
+function runTest() {
+  [
+    { observe: div,            target: div, subtree: false },
+    { observe: div.parentNode, target: div, subtree: true  },
+  ].forEach(aOptions => {
+
+    var e = aOptions.target;
+
+    promise_test(t => {
+      setupAsynchronousObserver(t, aOptions);
+      // Clear all styles once test finished since we re-use the same element
+      // in all test cases.
+      t.add_cleanup(() => {
+        e.style = "";
+        flushComputedStyle(e);
+      });
+
+      // Start a transition.
+      e.style = "transition: background-color 100s; background-color: lime;";
+
+      // Register for the end of the transition.
+      var transitionEnd = await_event(e, "transitionend");
+
+      // The transition should cause the creation of a single Animation.
+      var animations = e.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after transition start");
+
+      // Wait for the single MutationRecord for the Animation addition to
+      // be delivered.
+      return waitForFrame().then(() => {
+        assert_records([{ added: animations, changed: [], removed: [] }],
+                       "records after transition start");
+
+        // Advance until near the end of the transition, then wait for it to
+        // finish.
+        animations[0].currentTime = 99900;
+      }).then(() => {
+        return transitionEnd;
+      }).then(() => {
+        // After the transition has finished, the Animation should disappear.
+        assert_equals(e.getAnimations().length, 0,
+           "getAnimations().length after transition end");
+
+        // Wait for the change MutationRecord for seeking the Animation to be
+        // delivered, followed by the the removal MutationRecord.
+        return waitForFrame();
+      }).then(() => {
+        assert_records([{ added: [], changed: animations, removed: [] },
+                        { added: [], changed: [], removed: animations }],
+                       "records after transition end");
+      });
+    }, `single_transition ${aOptions.subtree ? ': subtree' : ''}`);
+
+    // Test that starting a single animation that completes normally
+    // dispatches an added notification and then a removed notification.
+    promise_test(t => {
+      setupAsynchronousObserver(t, aOptions);
+      t.add_cleanup(() => {
+        e.style = "";
+        flushComputedStyle(e);
+      });
+
+      // Start an animation.
+      e.style = "animation: anim 100s;";
+
+      // Register for the end of the animation.
+      var animationEnd = await_event(e, "animationend");
+
+      // The animation should cause the creation of a single Animation.
+      var animations = e.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      // Wait for the single MutationRecord for the Animation addition to
+      // be delivered.
+      return waitForFrame().then(() => {
+        assert_records([{ added: animations, changed: [], removed: [] }],
+                       "records after animation start");
+
+        // Advance until near the end of the animation, then wait for it to finish.
+        animations[0].currentTime = 99900;
+        return animationEnd;
+      }).then(() => {
+        // After the animation has finished, the Animation should disappear.
+        assert_equals(e.getAnimations().length, 0,
+          "getAnimations().length after animation end");
+
+        // Wait for the change MutationRecord from seeking the Animation to
+        // be delivered, followed by a further MutationRecord for the Animation
+        // removal.
+        return waitForFrame();
+      }).then(() => {
+        assert_records([{ added: [], changed: animations, removed: [] },
+                        { added: [], changed: [], removed: animations }],
+                       "records after animation end");
+      });
+    }, `single_animation ${aOptions.subtree ? ': subtree' : ''}`);
+
+    // Test that starting a single animation that is cancelled by updating
+    // the animation-fill-mode property dispatches an added notification and
+    // then a removed notification.
+    promise_test(t => {
+      setupAsynchronousObserver(t, aOptions);
+      t.add_cleanup(() => {
+        e.style = "";
+        flushComputedStyle(e);
+      });
+
+      // Start a short, filled animation.
+      e.style = "animation: anim 100s forwards;";
+
+      // Register for the end of the animation.
+      var animationEnd = await_event(e, "animationend");
+
+      // The animation should cause the creation of a single Animation.
+      var animations = e.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      // Wait for the single MutationRecord for the Animation addition to
+      // be delivered.
+      return waitForFrame().then(() => {
+        assert_records([{ added: animations, changed: [], removed: [] }],
+                       "records after animation start");
+
+        // Advance until near the end of the animation, then wait for it to finish.
+        animations[0].currentTime = 99900;
+        return animationEnd;
+      }).then(() => {
+        // The only MutationRecord at this point should be the change from
+        // seeking the Animation.
+        assert_records([{ added: [], changed: animations, removed: [] }],
+                       "records after animation starts filling");
+
+        // Cancel the animation by setting animation-fill-mode.
+        e.style.animationFillMode = "none";
+        // Explicitly flush style to make sure the above style change happens.
+        // Normally we don't need explicit style flush if there is a waitForFrame()
+        // call but in this particular case we are in the middle of animation events'
+        // callback handling and requestAnimationFrame handling so that we have no
+        // chance to process styling even after the requestAnimationFrame handling.
+        flushComputedStyle(e);
+
+        // Wait for the single MutationRecord for the Animation removal to
+        // be delivered.
+        return waitForFrame();
+      }).then(() => {
+        assert_records([{ added: [], changed: [], removed: animations }],
+                       "records after animation end");
+      });
+    }, `single_animation_cancelled_fill ${aOptions.subtree ? ': subtree' : ''}`);
+
+    // Test that calling finish() on a paused (but otherwise finished) animation
+    // dispatches a changed notification.
+    promise_test(t => {
+      setupAsynchronousObserver(t, aOptions);
+      t.add_cleanup(() => {
+        e.style = "";
+        flushComputedStyle(e);
+      });
+
+      // Start a long animation
+      e.style = "animation: anim 100s forwards";
+
+      // The animation should cause the creation of a single Animation.
+      var animations = e.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      // Wait for the single MutationRecord for the Animation addition to
+      // be delivered.
+      return waitForFrame().then(() => {
+        assert_records([{ added: animations, changed: [], removed: [] }],
+                        "records after animation start");
+
+        // Wait until the animation is playing.
+        return animations[0].ready;
+      }).then(() => {
+        // Finish and pause.
+        animations[0].finish();
+        animations[0].pause();
+
+        // Wait for the pause to complete.
+        return animations[0].ready;
+      }).then(() => {
+        assert_true(
+          !animations[0].pending && animations[0].playState === "paused",
+          "playState after finishing and pausing");
+
+        // We should have two MutationRecords for the Animation changes:
+        // one for the finish, one for the pause.
+        assert_records([{ added: [], changed: animations, removed: [] },
+                        { added: [], changed: animations, removed: [] }],
+                        "records after finish() and pause()");
+
+        // Call finish() again.
+        animations[0].finish();
+        assert_equals(animations[0].playState, "finished",
+          "playState after finishing from paused state");
+
+        // Wait for the single MutationRecord for the Animation change to
+        // be delivered. Even though the currentTime does not change, the
+        // playState will change.
+        return waitForFrame();
+      }).then(() => {
+        assert_records([{ added: [], changed: animations, removed: [] }],
+                        "records after finish() and pause()");
+
+        // Cancel the animation.
+        e.style = "";
+
+        // Wait for the single removal notification.
+        return waitForFrame();
+      }).then(() => {
+        assert_records([{ added: [], changed: [], removed: animations }],
+                        "records after animation end");
+      });
+    }, `finish_from_pause ${aOptions.subtree ? ': subtree' : ''}`);
+
+    // Test that calling play() on a paused Animation dispatches a changed
+    // notification.
+    promise_test(t => {
+      setupAsynchronousObserver(t, aOptions);
+      t.add_cleanup(() => {
+        e.style = "";
+        flushComputedStyle(e);
+      });
+
+      // Start a long, paused animation
+      e.style = "animation: anim 100s paused";
+
+      // The animation should cause the creation of a single Animation.
+      var animations = e.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      // Wait for the single MutationRecord for the Animation addition to
+      // be delivered.
+      return waitForFrame().then(() => {
+        assert_records([{ added: animations, changed: [], removed: [] }],
+                        "records after animation start");
+
+        // Wait until the animation is ready
+        return animations[0].ready;
+      }).then(() => {
+        // Play
+        animations[0].play();
+
+        // Wait for the single MutationRecord for the Animation change to
+        // be delivered.
+        return animations[0].ready;
+      }).then(() => {
+        assert_records([{ added: [], changed: animations, removed: [] }],
+                        "records after play()");
+
+        // Redundant play
+        animations[0].play();
+
+        // Wait to ensure no change is dispatched
+        return waitForFrame();
+      }).then(() => {
+        assert_records([], "records after redundant play()");
+
+        // Cancel the animation.
+        e.style = "";
+
+        // Wait for the single removal notification.
+        return waitForFrame();
+      }).then(() => {
+        assert_records([{ added: [], changed: [], removed: animations }],
+                        "records after animation end");
+      });
+    }, `play ${aOptions.subtree ? ': subtree' : ''}`);
+
+    // Test that a non-cancelling change to an animation followed immediately by a
+    // cancelling change will only send an animation removal notification.
+    promise_test(t => {
+      setupAsynchronousObserver(t, aOptions);
+      t.add_cleanup(() => {
+        e.style = "";
+        flushComputedStyle(e);
+      });
+
+      // Start a long animation.
+      e.style = "animation: anim 100s;";
+
+      // The animation should cause the creation of a single Animation.
+      var animations = e.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      // Wait for the single MutationRecord for the Animation addition to
+      // be delivered.
+      return waitForFrame().then(() => {;
+        assert_records([{ added: animations, changed: [], removed: [] }],
+                       "records after animation start");
+
+        // Update the animation's delay such that it is still running.
+        e.style.animationDelay = "-1s";
+
+        // Then cancel the animation by updating its duration.
+        e.style.animationDuration = "0.5s";
+
+        // We should get a single removal notification.
+        return waitForFrame();
+      }).then(() => {
+        assert_records([{ added: [], changed: [], removed: animations }],
+                       "records after animation end");
+      });
+    }, `coalesce_change_cancel ${aOptions.subtree ? ': subtree' : ''}`);
+
+  });
+}
+
+promise_test(t => {
+  setupAsynchronousObserver(t, { observe: div, subtree: true });
+  t.add_cleanup(() => {
+    div.style = "";
+    flushComputedStyle(div);
+  });
+
+  // Add style for pseudo elements
+  var extraStyle = document.createElement('style');
+  document.head.appendChild(extraStyle);
+  var sheet = extraStyle.sheet;
+  var rules = { ".before::before": "animation: anim 100s; content: '';",
+                ".after::after"  : "animation: anim 100s, anim 100s; " +
+                                   "content: '';"};
+  for (var selector in rules) {
+    sheet.insertRule(selector + '{' + rules[selector] + '}',
+                     sheet.cssRules.length);
+  }
+
+  // Create a tree with two children:
+  //
+  //          div
+  //       (::before)
+  //       (::after)
+  //        /     \
+  //   childA      childB(::before)
+  var childA = document.createElement("div");
+  var childB = document.createElement("div");
+
+  div.appendChild(childA);
+  div.appendChild(childB);
+
+  // Start an animation on each (using order: childB, div, childA)
+  //
+  // We include multiple animations on some nodes so that we can test batching
+  // works as expected later in this test.
+  childB.style = "animation: anim 100s";
+  div.style    = "animation: anim 100s, anim 100s, anim 100s";
+  childA.style = "animation: anim 100s, anim 100s";
+
+  // Start animations targeting to pseudo element of div and childB.
+  childB.classList.add("before");
+  div.classList.add("after");
+  div.classList.add("before");
+
+  // Check all animations we have in this document
+  var docAnims = document.getAnimations();
+  assert_equals(docAnims.length, 10, "total animations");
+
+  var divAnimations = div.getAnimations();
+  var childAAnimations = childA.getAnimations();
+  var childBAnimations = childB.getAnimations();
+
+  var divBeforeAnimations =
+    docAnims.filter(x => (x.effect.target == div &&
+                          x.effect.pseudoElement == "::before"));
+  var divAfterAnimations =
+    docAnims.filter(x => (x.effect.target == div &&
+                          x.effect.pseudoElement == "::after"));
+  var childBPseudoAnimations =
+    docAnims.filter(x => (x.effect.target == childB &&
+                          x.effect.pseudoElement == "::before"));
+
+  var seekRecords;
+  // The order in which we get the corresponding records is currently
+  // based on the order we visit these nodes when updating styles.
+  //
+  // That is because we don't do any document-level batching of animation
+  // mutation records when we flush styles. We may introduce that in the
+  // future but for now all we are interested in testing here is that the
+  // right records are generated, but we allow them to occur in any order.
+  return waitForFrame().then(() => {
+    assert_records_any_order(
+      [{ added: divAfterAnimations, changed: [], removed: [] },
+       { added: childAAnimations, changed: [], removed: [] },
+       { added: childBAnimations, changed: [], removed: [] },
+       { added: childBPseudoAnimations, changed: [], removed: [] },
+       { added: divAnimations, changed: [], removed: [] },
+       { added: divBeforeAnimations, changed: [], removed: [] }],
+      "records after simultaneous animation start");
+
+    // The one case where we *do* currently perform document-level (or actually
+    // timeline-level) batching is when animations are updated from a refresh
+    // driver tick. In particular, this means that when animations finish
+    // naturally the removed records should be dispatched according to the
+    // position of the elements in the tree.
+
+    // First, flatten the set of animations. we put the animations targeting to
+    // pseudo elements last. (Actually, we don't care the order in the list.)
+    var animations = [ ...divAnimations,
+                       ...childAAnimations,
+                       ...childBAnimations,
+                       ...divBeforeAnimations,
+                       ...divAfterAnimations,
+                       ...childBPseudoAnimations ];
+
+    // Fast-forward to *just* before the end of the animation.
+    animations.forEach(animation => animation.currentTime = 99999);
+
+    // Prepare the set of expected change MutationRecords, one for each
+    // animation that was seeked.
+    seekRecords = animations.map(
+      p => ({ added: [], changed: [p], removed: [] })
+    );
+
+    return await_event(div, "animationend");
+  }).then(() => {
+    // After the changed notifications, which will be dispatched in the order that
+    // the animations were seeked, we should get removal MutationRecords in order
+    // (div, div::before, div::after), childA, (childB, childB::before).
+    // Note: The animations targeting to the pseudo element are appended after
+    //       the animations of its parent element.
+    divAnimations = [ ...divAnimations,
+                      ...divBeforeAnimations,
+                      ...divAfterAnimations ];
+    childBAnimations = [ ...childBAnimations, ...childBPseudoAnimations ];
+    assert_records(seekRecords.concat(
+                     { added: [], changed: [], removed: divAnimations },
+                     { added: [], changed: [], removed: childAAnimations },
+                     { added: [], changed: [], removed: childBAnimations }),
+                   "records after finishing");
+
+    // Clean up
+    div.classList.remove("before");
+    div.classList.remove("after");
+    div.style = "";
+    childA.remove();
+    childB.remove();
+    extraStyle.remove();
+  });
+}, "tree_ordering: subtree");
+
+// Test that animations removed by auto-removal trigger an event
+promise_test(async t => {
+  setupAsynchronousObserver(t, { observe: div, subtree: false });
+
+  // Start two animations such that one will be auto-removed
+  const animA = div.animate(
+    { opacity: 1 },
+    { duration: 100 * MS_PER_SEC, fill: 'forwards' }
+  );
+  const animB = div.animate(
+    { opacity: 1 },
+    { duration: 100 * MS_PER_SEC, fill: 'forwards' }
+  );
+
+  // Wait for the MutationRecords corresponding to each addition.
+  await waitForNextFrame();
+
+  assert_records(
+    [
+      { added: [animA], changed: [], removed: [] },
+      { added: [animB], changed: [], removed: [] },
+    ],
+    'records after animation start'
+  );
+
+  // Finish the animations -- this should cause animA to be replaced, and
+  // automatically removed.
+  animA.finish();
+  animB.finish();
+
+  // Wait for the MutationRecords corresponding to the timing changes and the
+  // subsequent removal to be delivered.
+  await waitForNextFrame();
+
+  assert_records(
+    [
+      { added: [], changed: [animA], removed: [] },
+      { added: [], changed: [animB], removed: [] },
+      { added: [], changed: [], removed: [animA] },
+    ],
+    'records after finishing'
+  );
+
+  // Restore animA.
+  animA.persist();
+
+  // Wait for the MutationRecord corresponding to the re-addition of animA.
+  await waitForNextFrame();
+
+  assert_records(
+    [{ added: [animA], changed: [], removed: [] }],
+    'records after persisting'
+  );
+
+  // Tidy up
+  animA.cancel();
+  animB.cancel();
+
+  await waitForNextFrame();
+
+  assert_records(
+    [
+      { added: [], changed: [], removed: [animA] },
+      { added: [], changed: [], removed: [animB] },
+    ],
+    'records after tidying up end'
+  );
+}, 'Animations automatically removed are reported');
+
+setup({explicit_done: true});
+SpecialPowers.pushPrefEnv(
+  {
+    set: [
+      ["dom.animations-api.autoremove.enabled", true],
+      ["dom.animations-api.implicit-keyframes.enabled", true],
+    ],
+  },
+  function() {
+    runTest();
+    done();
+  }
+);
+</script>
diff --git a/dom/animation/test/chrome/test_animation_observers_sync.html b/dom/animation/test/chrome/test_animation_observers_sync.html
new file mode 100644
index 0000000000..7a890fd2f4
--- /dev/null
+++ b/dom/animation/test/chrome/test_animation_observers_sync.html
@@ -0,0 +1,1587 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>
+Test chrome-only MutationObserver animation notifications (sync tests)
+</title>
+<!--
+
+  This file contains synchronous tests for animation mutation observers.
+
+  In general we prefer to write synchronous tests since they are less likely to
+  timeout when run on automation. Tests that require asynchronous steps (e.g.
+  waiting on events) should be added to test_animations_observers_async.html
+  instead.
+
+-->
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+<div id="log"></div>
+<style>
+@keyframes anim {
+  to { transform: translate(100px); }
+}
+@keyframes anotherAnim {
+  to { transform: translate(0px); }
+}
+</style>
+<script>
+
+/**
+ * Return a new MutationObserver which observing |target| element
+ * with { animations: true, subtree: |subtree| } option.
+ *
+ * NOTE: This observer should be used only with takeRecords(). If any of
+ * MutationRecords are observed in the callback of the MutationObserver,
+ * it will raise an assertion.
+ */
+function setupSynchronousObserver(t, target, subtree) {
+  var observer = new MutationObserver(records => {
+    assert_unreached("Any MutationRecords should not be observed in this " +
+                     "callback");
+  });
+  t.add_cleanup(() => {
+    observer.disconnect();
+  });
+  observer.observe(target, { animations: true, subtree });
+  return observer;
+}
+
+function assert_record_list(actual, expected, desc, index, listName) {
+  assert_equals(actual.length, expected.length,
+                `${desc} - record[${index}].${listName} length`);
+  if (actual.length != expected.length) {
+    return;
+  }
+  for (var i = 0; i < actual.length; i++) {
+    assert_not_equals(actual.indexOf(expected[i]), -1,
+       `${desc} - record[${index}].${listName} contains expected Animation`);
+  }
+}
+
+function assert_equals_records(actual, expected, desc) {
+  assert_equals(actual.length, expected.length, `${desc} - number of records`);
+  if (actual.length != expected.length) {
+    return;
+  }
+  for (var i = 0; i < actual.length; i++) {
+    assert_record_list(actual[i].addedAnimations,
+                       expected[i].added, desc, i, "addedAnimations");
+    assert_record_list(actual[i].changedAnimations,
+                       expected[i].changed, desc, i, "changedAnimations");
+    assert_record_list(actual[i].removedAnimations,
+                       expected[i].removed, desc, i, "removedAnimations");
+  }
+}
+
+function runTest() {
+  [ { subtree: false },
+    { subtree: true }
+  ].forEach(aOptions => {
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] }, 200 * MS_PER_SEC);
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.updateTiming({ duration: 100 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after duration is changed");
+
+      anim.effect.updateTiming({ duration: 100 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning same value");
+
+      anim.currentTime = anim.effect.getComputedTiming().duration * 2;
+      anim.finish();
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [anim] }],
+        "records after animation end");
+
+      anim.effect.updateTiming({
+        duration: anim.effect.getComputedTiming().duration * 3
+      });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation restarted");
+
+      anim.effect.updateTiming({ duration: 'auto' });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [anim] }],
+        "records after duration set \"auto\"");
+
+      anim.effect.updateTiming({ duration: 'auto' });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning same value \"auto\"");
+    }, "change_duration_and_currenttime");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.updateTiming({ endDelay: 10 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after endDelay is changed");
+
+      anim.effect.updateTiming({ endDelay: 10 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning same value");
+
+      anim.currentTime = 109 * MS_PER_SEC;
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [anim] }],
+        "records after currentTime during endDelay");
+
+      anim.effect.updateTiming({ endDelay: -110 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning negative value");
+    }, "change_enddelay_and_currenttime");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] },
+                             { duration: 100 * MS_PER_SEC,
+                               endDelay: -100 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after animation is added");
+    }, "zero_end_time");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.updateTiming({ iterations: 2 });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after iterations is changed");
+
+      anim.effect.updateTiming({ iterations: 2 });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning same value");
+
+      anim.effect.updateTiming({ iterations: 0 });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [anim] }],
+        "records after animation end");
+
+      anim.effect.updateTiming({ iterations: Infinity });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation restarted");
+    }, "change_iterations");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.updateTiming({ delay: 100 });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after delay is changed");
+
+      anim.effect.updateTiming({ delay: 100 });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning same value");
+
+      anim.effect.updateTiming({ delay: -100 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [anim] }],
+        "records after animation end");
+
+      anim.effect.updateTiming({ delay: 0 });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation restarted");
+    }, "change_delay");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] },
+                             { duration: 100 * MS_PER_SEC,
+                               easing: "steps(2, start)" });
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.updateTiming({ easing: "steps(2, end)" });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after easing is changed");
+
+      anim.effect.updateTiming({ easing: "steps(2, end)" });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning same value");
+    }, "change_easing");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] },
+                             { duration: 100, delay: -100 });
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning negative value");
+    }, "negative_delay_in_constructor");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var effect = new KeyframeEffect(null,
+                                      { opacity: [ 0, 1 ] },
+                                      { duration: 100 * MS_PER_SEC });
+      var anim = new Animation(effect, document.timeline);
+      anim.play();
+      assert_equals_records(observer.takeRecords(),
+        [], "no records after animation is added");
+    }, "create_animation_without_target");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] },
+                             { duration: 100 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.target = div;
+      assert_equals_records(observer.takeRecords(),
+        [], "no records after setting the same target");
+
+      anim.effect.target = null;
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [anim] }],
+        "records after setting null");
+
+      anim.effect.target = null;
+      assert_equals_records(observer.takeRecords(),
+        [], "records after setting redundant null");
+    }, "set_redundant_animation_target");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] },
+                             { duration: 100 * MS_PER_SEC });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect = null;
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [anim] }],
+        "records after animation is removed");
+    }, "set_null_animation_effect");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = new Animation();
+      anim.play();
+      anim.effect = new KeyframeEffect(div, { opacity: [ 0, 1 ] },
+                                       100 * MS_PER_SEC);
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+    }, "set_effect_on_null_effect_animation");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ marginLeft: [ "0px", "100px" ] },
+                             100 * MS_PER_SEC);
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect = new KeyframeEffect(div, { opacity: [ 0, 1 ] },
+                                       100 * MS_PER_SEC);
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after replace effects");
+    }, "replace_effect_targeting_on_the_same_element");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ marginLeft: [ "0px", "100px" ] },
+                             100 * MS_PER_SEC);
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.currentTime = 60 * MS_PER_SEC;
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after animation is changed");
+
+      anim.effect = new KeyframeEffect(div, { opacity: [ 0, 1 ] },
+                                       50 * MS_PER_SEC);
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [anim] }],
+        "records after replacing effects");
+    }, "replace_effect_targeting_on_the_same_element_not_in_effect");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ }, 100 * MS_PER_SEC);
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.composite = "add";
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after composite is changed");
+
+      anim.effect.composite = "add";
+      assert_equals_records(observer.takeRecords(),
+        [], "no record after setting the same composite");
+
+    }, "set_composite");
+
+    // Test that starting a single animation that is cancelled by calling
+    // cancel() dispatches an added notification and then a removed
+    // notification.
+    test(t => {
+      var div = addDiv(t, { style: "animation: anim 100s forwards" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      animations[0].cancel();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+
+      // Re-trigger the animation.
+      animations[0].play();
+
+      // Single MutationRecord for the Animation (re-)addition.
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+    }, "single_animation_cancelled_api");
+
+    // Test that updating a property on the Animation object dispatches a changed
+    // notification.
+    [
+      { prop: "playbackRate", val: 0.5 },
+      { prop: "startTime",    val: 50 * MS_PER_SEC },
+      { prop: "currentTime",  val: 50 * MS_PER_SEC },
+    ].forEach(aChangeTest => {
+      test(t => {
+        // We use a forwards fill mode so that even if the change we make causes
+        // the animation to become finished, it will still be "relevant" so we
+        // won't mark it as removed.
+        var div = addDiv(t, { style: "animation: anim 100s forwards" });
+        var observer =
+          setupSynchronousObserver(t,
+                                   aOptions.subtree ? div.parentNode : div,
+                                   aOptions.subtree);
+
+        var animations = div.getAnimations();
+        assert_equals(animations.length, 1,
+          "getAnimations().length after animation start");
+
+        assert_equals_records(observer.takeRecords(),
+          [{ added: animations, changed: [], removed: [] }],
+          "records after animation start");
+
+        // Update the property.
+        animations[0][aChangeTest.prop] = aChangeTest.val;
+
+        // Make a redundant change.
+        animations[0][aChangeTest.prop] = animations[0][aChangeTest.prop];
+
+        assert_equals_records(observer.takeRecords(),
+          [{ added: [], changed: animations, removed: [] }],
+          "records after animation property change");
+      }, `single_animation_api_change_${aChangeTest.prop}`);
+    });
+
+    // Test that making a redundant change to currentTime while an Animation
+    // is pause-pending still generates a change MutationRecord since setting
+    // the currentTime to any value in this state aborts the pending pause.
+    test(t => {
+      var div = addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      animations[0].pause();
+
+      // We are now pause-pending. Even if we make a redundant change to the
+      // currentTime, we should still get a change record because setting the
+      // currentTime while pause-pending has the effect of cancelling a pause.
+      animations[0].currentTime = animations[0].currentTime;
+
+      // Two MutationRecords for the Animation changes: one for pausing, one
+      // for aborting the pause.
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] },
+         { added: [], changed: animations, removed: [] }],
+        "records after pausing then seeking");
+    }, "change_currentTime_while_pause_pending");
+
+    // Test that calling finish() on a forwards-filling Animation dispatches
+    // a changed notification.
+    test(t => {
+      var div = addDiv(t, { style: "animation: anim 100s forwards" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      animations[0].finish();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] }],
+        "records after finish()");
+
+      // Redundant finish.
+      animations[0].finish();
+
+      // Ensure no change records.
+      assert_equals_records(observer.takeRecords(),
+        [], "records after redundant finish()");
+    }, "finish_with_forwards_fill");
+
+    // Test that calling finish() on an Animation that does not fill forwards,
+    // dispatches a removal notification.
+    test(t => {
+      var div = addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      animations[0].finish();
+
+      // Single MutationRecord for the Animation removal.
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after finishing");
+    }, "finish_without_fill");
+
+    // Test that calling finish() on a forwards-filling Animation dispatches
+    test(t => {
+      var div = addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animation = div.getAnimations()[0];
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [animation], changed: [], removed: []}],
+        "records after creation");
+      animation.id = "new id";
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [animation], removed: []}],
+        "records after id is changed");
+
+      animation.id = "new id";
+      assert_equals_records(observer.takeRecords(),
+        [], "records after assigning same value with id");
+    }, "change_id");
+
+    // Test that calling reverse() dispatches a changed notification.
+    test(t => {
+      var div = addDiv(t, { style: "animation: anim 100s both" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      animations[0].reverse();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] }],
+        "records after calling reverse()");
+    }, "reverse");
+
+    // Test that calling reverse() does *not* dispatch a changed notification
+    // when playbackRate == 0.
+    test(t => {
+      var div = addDiv(t, { style: "animation: anim 100s both" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Seek to the middle and set playbackRate to zero.
+      animations[0].currentTime = 50 * MS_PER_SEC;
+      animations[0].playbackRate = 0;
+
+      // Two MutationRecords, one for each change.
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] },
+         { added: [], changed: animations, removed: [] }],
+        "records after seeking and setting playbackRate");
+
+      animations[0].reverse();
+
+      // We should get no notifications.
+      assert_equals_records(observer.takeRecords(),
+        [], "records after calling reverse()");
+    }, "reverse_with_zero_playbackRate");
+
+    // Test that reverse() on an Animation does *not* dispatch a changed
+    // notification when it throws an exception.
+    test(t => {
+      // Start an infinite animation
+      var div = addDiv(t, { style: "animation: anim 10s infinite" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Shift the animation into the future such that when we call reverse
+      // it will try to seek to the (infinite) end.
+      animations[0].startTime = 100 * MS_PER_SEC;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] }],
+        "records after adjusting startTime");
+
+      // Reverse: should throw
+      assert_throws('InvalidStateError', () => {
+        animations[0].reverse();
+      }, 'reverse() on future infinite animation throws an exception');
+
+      // We should get no notifications.
+      assert_equals_records(observer.takeRecords(),
+        [], "records after calling reverse()");
+    }, "reverse_with_exception");
+
+    // Test that attempting to start an animation that should already be finished
+    // does not send any notifications.
+    test(t => {
+      // Start an animation that should already be finished.
+      var div = addDiv(t, { style: "animation: anim 1s -2s;" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause no Animations to be created.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 0,
+        "getAnimations().length after animation start");
+
+      // And we should get no notifications.
+      assert_equals_records(observer.takeRecords(),
+        [], "records after attempted animation start");
+    }, "already_finished");
+
+    test(t => {
+      var div = addDiv(t, { style: "animation: anim 100s, anotherAnim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var animations = div.getAnimations();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: []}],
+        "records after creation");
+
+      div.style.animation = "anotherAnim 100s, anim 100s";
+      animations = div.getAnimations();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: []}],
+        "records after the order is changed");
+
+      div.style.animation = "anotherAnim 100s, anim 100s";
+
+      assert_equals_records(observer.takeRecords(),
+        [], "no records after applying the same order");
+    }, "animtion_order_change");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] },
+                             { duration: 100 * MS_PER_SEC,
+                               iterationComposite: 'replace' });
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.iterationComposite = 'accumulate';
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after iterationComposite is changed");
+
+      anim.effect.iterationComposite = 'accumulate';
+      assert_equals_records(observer.takeRecords(),
+        [], "no record after setting the same iterationComposite");
+
+    }, "set_iterationComposite");
+
+    test(t => {
+      var div = addDiv(t);
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      var anim = div.animate({ opacity: [ 0, 1 ] },
+                             { duration: 100 * MS_PER_SEC });
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [anim], changed: [], removed: [] }],
+        "records after animation is added");
+
+      anim.effect.setKeyframes({ opacity: 0.1 });
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after keyframes are changed");
+
+      anim.effect.setKeyframes({ opacity: 0.1 });
+      assert_equals_records(observer.takeRecords(),
+        [], "no record after setting the same keyframes");
+
+      anim.effect.setKeyframes(null);
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [anim], removed: [] }],
+        "records after keyframes are set to empty");
+
+    }, "set_keyframes");
+
+    // Test that starting a single transition that is cancelled by resetting
+    // the transition-property property dispatches an added notification and
+    // then a removed notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "transition: background-color 100s; " +
+                           "background-color: yellow;" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      getComputedStyle(div).transitionProperty;
+      div.style.backgroundColor = "lime";
+
+      // The transition should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after transition start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after transition start");
+
+      // Cancel the transition by setting transition-property.
+      div.style.transitionProperty = "none";
+      getComputedStyle(div).transitionProperty;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after transition end");
+    }, "single_transition_cancelled_property");
+
+    // Test that starting a single transition that is cancelled by setting
+    // style to the currently animated value dispatches an added
+    // notification and then a removed notification.
+    test(t => {
+      // A long transition with a predictable value.
+      var div =
+        addDiv(t, { style: "transition: z-index 100s -51s; " +
+                           "z-index: 10;" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+      getComputedStyle(div).transitionProperty;
+      div.style.zIndex = "100";
+
+      // The transition should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after transition start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after transition start");
+
+      // Cancel the transition by setting the current animation value.
+      let value = "83";
+      assert_equals(getComputedStyle(div).zIndex, value,
+        "half-way transition value");
+      div.style.zIndex = value;
+      getComputedStyle(div).transitionProperty;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after transition end");
+    }, "single_transition_cancelled_value");
+
+    // Test that starting a single transition that is cancelled by setting
+    // style to a non-interpolable value dispatches an added notification
+    // and then a removed notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "transition: line-height 100s; " +
+                           "line-height: 16px;" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      getComputedStyle(div).transitionProperty;
+      div.style.lineHeight = "100px";
+
+      // The transition should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after transition start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after transition start");
+
+      // Cancel the transition by setting line-height to a non-interpolable value.
+      div.style.lineHeight = "normal";
+      getComputedStyle(div).transitionProperty;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after transition end");
+    }, "single_transition_cancelled_noninterpolable");
+
+    // Test that starting a single transition and then reversing it
+    // dispatches an added notification, then a simultaneous removed and
+    // added notification, then a removed notification once finished.
+    test(t => {
+      var div =
+        addDiv(t, { style: "transition: background-color 100s step-start; " +
+                           "background-color: yellow;" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      getComputedStyle(div).transitionProperty;
+      div.style.backgroundColor = "lime";
+
+      var animations = div.getAnimations();
+
+      // The transition should cause the creation of a single Animation.
+      assert_equals(animations.length, 1,
+        "getAnimations().length after transition start");
+
+      var firstAnimation = animations[0];
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [firstAnimation], changed: [], removed: [] }],
+        "records after transition start");
+
+      firstAnimation.currentTime = 50 * MS_PER_SEC;
+
+      // Reverse the transition by setting the background-color back to its
+      // original value.
+      div.style.backgroundColor = "yellow";
+
+      // The reversal should cause the creation of a new Animation.
+      animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after transition reversal");
+
+      var secondAnimation = animations[0];
+
+      assert_true(firstAnimation != secondAnimation,
+        "second Animation should be different from the first");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [firstAnimation], removed: [] },
+         { added: [secondAnimation], changed: [], removed: [firstAnimation] }],
+        "records after transition reversal");
+
+      // Cancel the transition.
+      div.style.transitionProperty = "none";
+      getComputedStyle(div).transitionProperty;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: [secondAnimation] }],
+        "records after transition end");
+    }, "single_transition_reversed");
+
+    // Test that multiple transitions starting and ending on an element
+    // at the same time get batched up into a single MutationRecord.
+    test(t => {
+      var div =
+        addDiv(t, { style: "transition-duration: 100s; " +
+                           "transition-property: color, background-color, line-height" +
+                           "background-color: yellow; line-height: 16px" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+      getComputedStyle(div).transitionProperty;
+
+      div.style.backgroundColor = "lime";
+      div.style.color = "blue";
+      div.style.lineHeight = "24px";
+
+      // The transitions should cause the creation of three Animations.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 3,
+        "getAnimations().length after transition starts");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after transition starts");
+
+      assert_equals(animations.filter(p => p.playState == "running").length, 3,
+         "number of running Animations");
+
+      // Seek well into each animation.
+      animations.forEach(p => p.currentTime = 50 * MS_PER_SEC);
+
+      // Prepare the set of expected change MutationRecords, one for each
+      // animation that was seeked.
+      var seekRecords = animations.map(
+        p => ({ added: [], changed: [p], removed: [] })
+      );
+
+      // Cancel one of the transitions by setting transition-property.
+      div.style.transitionProperty = "background-color, line-height";
+
+      var colorAnimation  = animations.filter(p => p.playState != "running");
+      var otherAnimations = animations.filter(p => p.playState == "running");
+
+      assert_equals(colorAnimation.length, 1,
+        "number of non-running Animations after cancelling one");
+      assert_equals(otherAnimations.length, 2,
+        "number of running Animations after cancelling one");
+
+      assert_equals_records(observer.takeRecords(),
+        seekRecords.concat({ added: [], changed: [], removed: colorAnimation }),
+        "records after color transition end");
+
+      // Cancel the remaining transitions.
+      div.style.transitionProperty = "none";
+      getComputedStyle(div).transitionProperty;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: otherAnimations }],
+        "records after other transition ends");
+    }, "multiple_transitions");
+
+    // Test that starting a single animation that is cancelled by resetting
+    // the animation-name property dispatches an added notification and
+    // then a removed notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Cancel the animation by setting animation-name.
+      div.style.animationName = "none";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "single_animation_cancelled_name");
+
+    // Test that starting a single animation that is cancelled by updating
+    // the animation-duration property dispatches an added notification and
+    // then a removed notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Advance the animation by a second.
+      animations[0].currentTime += 1 * MS_PER_SEC;
+
+      // Cancel the animation by setting animation-duration to a value less
+      // than a second.
+      div.style.animationDuration = "0.1s";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] },
+         { added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "single_animation_cancelled_duration");
+
+    // Test that starting a single animation that is cancelled by updating
+    // the animation-delay property dispatches an added notification and
+    // then a removed notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Cancel the animation by setting animation-delay.
+      div.style.animationDelay = "-200s";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "single_animation_cancelled_delay");
+
+    // Test that starting a single animation that is cancelled by updating
+    // the animation-iteration-count property dispatches an added notification
+    // and then a removed notification.
+    test(t => {
+      // A short, repeated animation.
+      var div =
+        addDiv(t, { style: "animation: anim 0.5s infinite;" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Advance the animation until we are past the first iteration.
+      animations[0].currentTime += 1 * MS_PER_SEC;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] }],
+        "records after seeking animations");
+
+      // Cancel the animation by setting animation-iteration-count.
+      div.style.animationIterationCount = "1";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "single_animation_cancelled_iteration_count");
+
+    // Test that updating an animation property dispatches a changed notification.
+    [
+      { name: "duration",  prop: "animationDuration",       val: "200s"    },
+      { name: "timing",    prop: "animationTimingFunction", val: "linear"  },
+      { name: "iteration", prop: "animationIterationCount", val: "2"       },
+      { name: "direction", prop: "animationDirection",      val: "reverse" },
+      { name: "state",     prop: "animationPlayState",      val: "paused"  },
+      { name: "delay",     prop: "animationDelay",          val: "-1s"     },
+      { name: "fill",      prop: "animationFillMode",       val: "both"    },
+    ].forEach(aChangeTest => {
+      test(t => {
+        // Start a long animation.
+        var div = addDiv(t, { style: "animation: anim 100s;" });
+        var observer =
+          setupSynchronousObserver(t,
+                                   aOptions.subtree ? div.parentNode : div,
+                                   aOptions.subtree);
+
+        // The animation should cause the creation of a single Animation.
+        var animations = div.getAnimations();
+        assert_equals(animations.length, 1,
+          "getAnimations().length after animation start");
+
+        assert_equals_records(observer.takeRecords(),
+          [{ added: animations, changed: [], removed: [] }],
+          "records after animation start");
+
+        // Change a property of the animation such that it keeps running.
+        div.style[aChangeTest.prop] = aChangeTest.val;
+        getComputedStyle(div).animationName;
+
+        assert_equals_records(observer.takeRecords(),
+          [{ added: [], changed: animations, removed: [] }],
+          "records after animation change");
+
+        // Cancel the animation.
+        div.style.animationName = "none";
+        getComputedStyle(div).animationName;
+
+        assert_equals_records(observer.takeRecords(),
+          [{ added: [], changed: [], removed: animations }],
+          "records after animation end");
+      }, `single_animation_change_${aChangeTest.name}`);
+    });
+
+    // Test that calling finish() on a pause-pending (but otherwise finished)
+    // animation dispatches a changed notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "animation: anim 100s forwards" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Finish and pause.
+      animations[0].finish();
+      animations[0].pause();
+      assert_true(animations[0].pending && animations[0].playState === "paused",
+        "playState after finishing and calling pause()");
+
+      // Call finish() again to abort the pause
+      animations[0].finish();
+      assert_equals(animations[0].playState, "finished",
+        "playState after finishing again");
+
+      // Wait for three MutationRecords for the Animation changes to
+      // be delivered: one for each finish(), pause(), finish() operation.
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] },
+         { added: [], changed: animations, removed: [] },
+         { added: [], changed: animations, removed: [] }],
+        "records after finish(), pause(), finish()");
+
+      // Cancel the animation.
+      div.style = "";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "finish_from_pause_pending");
+
+    // Test that calling play() on a finished Animation that fills forwards
+    // dispatches a changed notification.
+    test(t => {
+      // Animation with a forwards fill
+      var div =
+        addDiv(t, { style: "animation: anim 100s forwards" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Seek to the end
+      animations[0].finish();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] }],
+        "records after finish()");
+
+      // Since we are filling forwards, calling play() should produce a
+      // change record since the animation remains relevant.
+      animations[0].play();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] }],
+        "records after play()");
+
+      // Cancel the animation.
+      div.style = "";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "play_filling_forwards");
+
+    // Test that calling pause() on an Animation dispatches a changed
+    // notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Pause
+      animations[0].pause();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] }],
+        "records after pause()");
+
+      // Redundant pause
+      animations[0].pause();
+
+      assert_equals_records(observer.takeRecords(),
+        [], "records after redundant pause()");
+
+      // Cancel the animation.
+      div.style = "";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "pause");
+
+    // Test that calling pause() on an Animation that is pause-pending
+    // does not dispatch an additional changed notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Pause
+      animations[0].pause();
+
+      // We are now pause-pending, but pause again
+      animations[0].pause();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] }],
+        "records after pause()");
+
+      // Cancel the animation.
+      div.style = "";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "pause_while_pause_pending");
+
+    // Test that calling play() on an Animation that is pause-pending
+    // dispatches a changed notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Pause
+      animations[0].pause();
+
+      // We are now pause-pending. If we play() now, we will abort the pause
+      animations[0].play();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: animations, removed: [] },
+        { added: [], changed: animations, removed: [] }],
+                      "records after aborting a pause()");
+
+      // Cancel the animation.
+      div.style = "";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "aborted_pause");
+
+    // Test that calling play() on a finished Animation that does *not* fill
+    // forwards dispatches an addition notification.
+    test(t => {
+      var div =
+        addDiv(t, { style: "animation: anim 100s" });
+      var observer =
+        setupSynchronousObserver(t,
+                                 aOptions.subtree ? div.parentNode : div,
+                                 aOptions.subtree);
+
+      // The animation should cause the creation of a single Animation.
+      var animations = div.getAnimations();
+      assert_equals(animations.length, 1,
+        "getAnimations().length after animation start");
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after animation start");
+
+      // Seek to the end
+      animations[0].finish();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after finish()");
+
+      // Since we are *not* filling forwards, calling play() is equivalent
+      // to creating a new animation since it becomes relevant again.
+      animations[0].play();
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: animations, changed: [], removed: [] }],
+        "records after play()");
+
+      // Cancel the animation.
+      div.style = "";
+      getComputedStyle(div).animationName;
+
+      assert_equals_records(observer.takeRecords(),
+        [{ added: [], changed: [], removed: animations }],
+        "records after animation end");
+    }, "play_after_finish");
+
+  });
+
+  test(t => {
+    var div = addDiv(t);
+    var observer = setupSynchronousObserver(t, div, true);
+
+    var child = document.createElement("div");
+    div.appendChild(child);
+
+    var anim1 = div.animate({ marginLeft: [ "0px", "50px" ] },
+                            100 * MS_PER_SEC);
+    var anim2 = child.animate({ marginLeft: [ "0px", "100px" ] },
+                              50 * MS_PER_SEC);
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [anim1], changed: [], removed: [] },
+       { added: [anim2], changed: [], removed: [] }],
+      "records after animation is added");
+
+    // After setting a new effect, we remove the current animation, anim1,
+    // because it is no longer attached to |div|, and then remove the previous
+    // animation, anim2. Finally, add back the anim1 which is in effect on
+    // |child| now. In addition, we sort them by tree order and they are
+    // batched.
+    anim1.effect = anim2.effect;
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [], changed: [], removed: [anim1] },       // div
+       { added: [anim1], changed: [], removed: [anim2] }], // child
+      "records after animation effects are changed");
+  }, "set_effect_with_previous_animation");
+
+  test(t => {
+    var div = addDiv(t);
+    var observer = setupSynchronousObserver(t, document, true);
+
+    var anim = div.animate({ opacity: [ 0, 1 ] },
+                           { duration: 100 * MS_PER_SEC });
+
+    var newTarget = document.createElement("div");
+
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [anim], changed: [], removed: [] }],
+      "records after animation is added");
+
+    anim.effect.target = null;
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [], changed: [], removed: [anim] }],
+      "records after setting null");
+
+    anim.effect.target = div;
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [anim], changed: [], removed: [] }],
+      "records after setting a target");
+
+    anim.effect.target = addDiv(t);
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [], changed: [], removed: [anim] },
+       { added: [anim], changed: [], removed: [] }],
+      "records after setting a different target");
+  }, "set_animation_target");
+
+  test(t => {
+    var div = addDiv(t);
+    var observer = setupSynchronousObserver(t, div, true);
+
+    var anim = div.animate({ opacity: [ 0, 1 ] },
+                           { duration: 200 * MS_PER_SEC,
+                             pseudoElement: '::before' });
+
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [anim], changed: [], removed: [] }],
+      "records after animation is added");
+
+    anim.effect.updateTiming({ duration: 100 * MS_PER_SEC });
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [], changed: [anim], removed: [] }],
+      "records after duration is changed");
+
+    anim.effect.updateTiming({ duration: 100 * MS_PER_SEC });
+    assert_equals_records(observer.takeRecords(),
+      [], "records after assigning same value");
+
+    anim.currentTime = anim.effect.getComputedTiming().duration * 2;
+    anim.finish();
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [], changed: [], removed: [anim] }],
+      "records after animation end");
+
+    anim.effect.updateTiming({
+      duration: anim.effect.getComputedTiming().duration * 3
+    });
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [anim], changed: [], removed: [] }],
+      "records after animation restarted");
+
+    anim.effect.updateTiming({ duration: "auto" });
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [], changed: [], removed: [anim] }],
+      "records after duration set \"auto\"");
+
+    anim.effect.updateTiming({ duration: "auto" });
+    assert_equals_records(observer.takeRecords(),
+      [], "records after assigning same value \"auto\"");
+  }, "change_duration_and_currenttime_on_pseudo_elements");
+
+  test(t => {
+    var div = addDiv(t);
+    var observer = setupSynchronousObserver(t, div, false);
+
+    var anim = div.animate({ opacity: [ 0, 1 ] },
+                           { duration: 100 * MS_PER_SEC });
+    var pAnim = div.animate({ opacity: [ 0, 1 ] },
+                            { duration: 100 * MS_PER_SEC,
+                              pseudoElement: "::before" });
+
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [anim], changed: [], removed: [] }],
+      "records after animation is added");
+
+    anim.finish();
+    pAnim.finish();
+
+    assert_equals_records(observer.takeRecords(),
+      [{ added: [], changed: [], removed: [anim] }],
+      "records after animation is finished");
+  }, "exclude_animations_targeting_pseudo_elements");
+}
+
+W3CTest.runner.expectAssertions(0, 12); // bug 1189015
+setup({explicit_done: true});
+SpecialPowers.pushPrefEnv(
+  {
+    set: [
+      ["dom.animations-api.core.enabled", true],
+      ["dom.animations-api.implicit-keyframes.enabled", true],
+      ["dom.animations-api.timelines.enabled", true],
+    ],
+  },
+  function() {
+    runTest();
+    done();
+  }
+);
+
+</script>
diff --git a/dom/animation/test/chrome/test_animation_performance_warning.html b/dom/animation/test/chrome/test_animation_performance_warning.html
new file mode 100644
index 0000000000..ca0572cfaa
--- /dev/null
+++ b/dom/animation/test/chrome/test_animation_performance_warning.html
@@ -0,0 +1,1692 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Bug 1196114 - Test metadata related to which animation properties
+       are running on the compositor</title>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+<style>
+.compositable {
+  /* Element needs geometry to be eligible for layerization */
+  width: 100px;
+  height: 100px;
+  background-color: white;
+}
+@keyframes fade {
+  from { opacity: 1 }
+  to   { opacity: 0 }
+}
+@keyframes translate {
+  from { transform: none }
+  to   { transform: translate(100px) }
+}
+</style>
+</head>
+<body>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1196114"
+  target="_blank">Mozilla Bug 1196114</a>
+<div id="log"></div>
+<script>
+'use strict';
+
+// This is used for obtaining localized strings.
+var gStringBundle;
+
+W3CTest.runner.requestLongerTimeout(2);
+
+const Services = SpecialPowers.Services;
+Services.locale.requestedLocales = ["en-US"];
+
+SpecialPowers.pushPrefEnv({ "set": [
+                            // Need to set devPixelsPerPx explicitly to gain
+                            // consistent pixel values in warning messages
+                            // regardless of platform DPIs.
+                            ["layout.css.devPixelsPerPx", 1],
+                            ["layout.animation.prerender.partial", false],
+                          ] },
+                          start);
+
+function compare_property_state(a, b) {
+  if (a.property > b.property) {
+    return -1;
+  } else if (a.property < b.property) {
+    return 1;
+  }
+  if (a.runningOnCompositor != b.runningOnCompositor) {
+    return a.runningOnCompositor ? 1 : -1;
+  }
+  return a.warning > b.warning ? -1 : 1;
+}
+
+function assert_animation_property_state_equals(actual, expected) {
+  assert_equals(actual.length, expected.length, 'Number of properties');
+
+  var sortedActual = actual.sort(compare_property_state);
+  var sortedExpected = expected.sort(compare_property_state);
+
+  for (var i = 0; i < sortedActual.length; i++) {
+    assert_equals(sortedActual[i].property,
+                  sortedExpected[i].property,
+                  'CSS property name should match');
+    assert_equals(sortedActual[i].runningOnCompositor,
+                  sortedExpected[i].runningOnCompositor,
+                  'runningOnCompositor property should match');
+    if (sortedExpected[i].warning instanceof RegExp) {
+      assert_regexp_match(sortedActual[i].warning,
+                          sortedExpected[i].warning,
+                          'warning message should match');
+    } else if (sortedExpected[i].warning) {
+      assert_equals(sortedActual[i].warning,
+                    gStringBundle.GetStringFromName(sortedExpected[i].warning),
+                    'warning message should match');
+    }
+  }
+}
+
+// Check that the animation is running on compositor and
+// warning property is not set for the CSS property regardless
+// expected values.
+function assert_all_properties_running_on_compositor(actual, expected) {
+  assert_equals(actual.length, expected.length);
+
+  var sortedActual = actual.sort(compare_property_state);
+  var sortedExpected = expected.sort(compare_property_state);
+
+  for (var i = 0; i < sortedActual.length; i++) {
+    assert_equals(sortedActual[i].property,
+                  sortedExpected[i].property,
+                  'CSS property name should match');
+    assert_true(sortedActual[i].runningOnCompositor,
+                'runningOnCompositor property should be true on ' +
+                sortedActual[i].property);
+    assert_not_exists(sortedActual[i], 'warning',
+                      'warning property should not be set');
+  }
+}
+
+function testBasicOperation() {
+  [
+    {
+      desc: 'animations on compositor',
+      frames: {
+        opacity: [0, 1]
+      },
+      expected: [
+        {
+          property: 'opacity',
+          runningOnCompositor: true
+        }
+      ]
+    },
+    {
+      desc: 'animations on main thread',
+      frames: {
+        zIndex: ['0', '999']
+      },
+      expected: [
+        {
+          property: 'z-index',
+          runningOnCompositor: false
+        }
+      ]
+    },
+    {
+      desc: 'animations on both threads',
+      frames: {
+        zIndex: ['0', '999'],
+        transform: ['translate(0px)', 'translate(100px)']
+      },
+      expected: [
+        {
+          property: 'z-index',
+          runningOnCompositor: false
+        },
+        {
+          property: 'transform',
+          runningOnCompositor: true
+        }
+      ]
+    },
+    {
+      desc: 'two animation properties on compositor thread',
+      frames: {
+        opacity: [0, 1],
+        transform: ['translate(0px)', 'translate(100px)']
+      },
+      expected: [
+        {
+          property: 'opacity',
+          runningOnCompositor: true
+        },
+        {
+          property: 'transform',
+          runningOnCompositor: true
+        }
+      ]
+    },
+    {
+      desc: 'two transform-like animation properties on compositor thread',
+      frames: {
+        transform: ['translate(0px)', 'translate(100px)'],
+        translate: ['0px', '100px']
+      },
+      expected: [
+        {
+          property: 'transform',
+          runningOnCompositor: true
+        },
+        {
+          property: 'translate',
+          runningOnCompositor: true
+        }
+      ]
+    },
+    {
+      desc: 'opacity on compositor with animation of geometric properties',
+      frames: {
+        width: ['100px', '200px'],
+        opacity: [0, 1]
+      },
+      expected: [
+        {
+          property: 'width',
+          runningOnCompositor: false
+        },
+        {
+          property: 'opacity',
+          runningOnCompositor: true
+        }
+      ]
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      var animation = addDivAndAnimate(t, { class: 'compositable' },
+                                       subtest.frames, 100 * MS_PER_SEC);
+      await waitForPaints();
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        subtest.expected);
+    }, subtest.desc);
+  });
+}
+
+// Test adding/removing a 'width' property on the same animation object.
+function testKeyframesWithGeometricProperties() {
+  [
+    {
+      desc: 'transform',
+      frames: {
+        transform: ['translate(0px)', 'translate(100px)']
+      },
+      expected: {
+        withoutGeometric: [
+          {
+            property: 'transform',
+            runningOnCompositor: true
+          }
+        ],
+        withGeometric: [
+          {
+            property: 'width',
+            runningOnCompositor: false
+          },
+          {
+            property: 'transform',
+            runningOnCompositor: false,
+            warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+          }
+        ]
+      }
+    },
+    {
+      desc: 'translate',
+      frames: {
+        translate: ['0px', '100px']
+      },
+      expected: {
+        withoutGeometric: [
+          {
+            property: 'translate',
+            runningOnCompositor: true
+          }
+        ],
+        withGeometric: [
+          {
+            property: 'width',
+            runningOnCompositor: false
+          },
+          {
+            property: 'translate',
+            runningOnCompositor: false,
+            warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+          }
+        ]
+      }
+    },
+    {
+      desc: 'opacity and transform-like properties',
+      frames: {
+        opacity: [0, 1],
+        transform: ['translate(0px)', 'translate(100px)'],
+        translate: ['0px', '100px']
+      },
+      expected: {
+        withoutGeometric: [
+          {
+            property: 'opacity',
+            runningOnCompositor: true
+          },
+          {
+            property: 'transform',
+            runningOnCompositor: true
+          },
+          {
+            property: 'translate',
+            runningOnCompositor: true
+          }
+        ],
+        withGeometric: [
+          {
+            property: 'width',
+            runningOnCompositor: false
+          },
+          {
+            property: 'opacity',
+            runningOnCompositor: true
+          },
+          {
+            property: 'transform',
+            runningOnCompositor: false,
+            warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+          },
+          {
+            property: 'translate',
+            runningOnCompositor: false,
+            warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+          }
+        ]
+      }
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      var animation = addDivAndAnimate(t, { class: 'compositable' },
+                                       subtest.frames, 100 * MS_PER_SEC);
+      await waitForPaints();
+
+      // First, a transform animation is running on compositor.
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        subtest.expected.withoutGeometric);
+
+      // Add a 'width' property.
+      var keyframes = animation.effect.getKeyframes();
+
+      keyframes[0].width = '100px';
+      keyframes[1].width = '200px';
+
+      animation.effect.setKeyframes(keyframes);
+      await waitForFrame();
+
+      // Now the transform animation is not running on compositor because of
+      // the 'width' property.
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        subtest.expected.withGeometric);
+
+      // Remove the 'width' property.
+      var keyframes = animation.effect.getKeyframes();
+
+      delete keyframes[0].width;
+      delete keyframes[1].width;
+
+      animation.effect.setKeyframes(keyframes);
+      await waitForFrame();
+
+      // Finally, the transform animation is running on compositor.
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        subtest.expected.withoutGeometric);
+    }, 'An animation has: ' + subtest.desc);
+  });
+}
+
+// Test that the expected set of geometric properties all block transform
+// animations.
+function testSetOfGeometricProperties() {
+  const geometricProperties = [
+    'width', 'height',
+    'top', 'right', 'bottom', 'left',
+    'margin-top', 'margin-right', 'margin-bottom', 'margin-left',
+    'padding-top', 'padding-right', 'padding-bottom', 'padding-left'
+  ];
+
+  geometricProperties.forEach(property => {
+    promise_test(async t => {
+      const keyframes = {
+        [propertyToIDL(property)]: [ '100px', '200px' ],
+        transform: [ 'translate(0px)', 'translate(100px)' ]
+      };
+      var animation = addDivAndAnimate(t, { class: 'compositable' },
+                                       keyframes, 100 * MS_PER_SEC);
+
+      await waitForPaints();
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [
+          {
+            property,
+            runningOnCompositor: false
+          },
+          {
+            property: 'transform',
+            runningOnCompositor: false,
+            warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+          }
+        ]);
+    }, `${property} is treated as a geometric property`);
+  });
+}
+
+// Performance warning tests that set and clear a style property.
+function testStyleChanges() {
+  [
+    {
+      desc: 'preserve-3d transform',
+      frames: {
+        transform: ['translate(0px)', 'translate(100px)']
+      },
+      style: 'transform-style: preserve-3d',
+      expected: [
+        {
+          property: 'transform',
+          runningOnCompositor: true,
+        }
+      ]
+    },
+    {
+      desc: 'preserve-3d translate',
+      frames: {
+        translate: ['0px', '100px']
+      },
+      style: 'transform-style: preserve-3d',
+      expected: [
+        {
+          property: 'translate',
+          runningOnCompositor: true,
+        }
+      ]
+    },
+    {
+      desc: 'transform with backface-visibility:hidden',
+      frames: {
+        transform: ['translate(0px)', 'translate(100px)']
+      },
+      style: 'backface-visibility: hidden;',
+      expected: [
+        {
+          property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformBackfaceVisibilityHidden'
+        }
+      ]
+    },
+    {
+      desc: 'translate with backface-visibility:hidden',
+      frames: {
+        translate: ['0px', '100px']
+      },
+      style: 'backface-visibility: hidden;',
+      expected: [
+        {
+          property: 'translate',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformBackfaceVisibilityHidden'
+        }
+      ]
+    },
+    {
+      desc: 'opacity and transform-like properties with preserve-3d',
+      frames: {
+        opacity: [0, 1],
+        transform: ['translate(0px)', 'translate(100px)'],
+        translate: ['0px', '100px']
+      },
+      style: 'transform-style: preserve-3d',
+      expected: [
+        {
+          property: 'opacity',
+          runningOnCompositor: true
+        },
+        {
+          property: 'transform',
+          runningOnCompositor: true,
+        },
+        {
+          property: 'translate',
+          runningOnCompositor: true,
+        }
+      ]
+    },
+    {
+      desc: 'opacity and transform-like properties with ' +
+            'backface-visibility:hidden',
+      frames: {
+        opacity: [0, 1],
+        transform: ['translate(0px)', 'translate(100px)'],
+        translate: ['0px', '100px']
+      },
+      style: 'backface-visibility: hidden;',
+      expected: [
+        {
+          property: 'opacity',
+          runningOnCompositor: true
+        },
+        {
+          property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformBackfaceVisibilityHidden'
+        },
+        {
+          property: 'translate',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformBackfaceVisibilityHidden'
+        }
+      ]
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      var animation = addDivAndAnimate(t, { class: 'compositable' },
+                                       subtest.frames, 100 * MS_PER_SEC);
+      await waitForPaints();
+      assert_all_properties_running_on_compositor(
+        animation.effect.getProperties(),
+        subtest.expected);
+      animation.effect.target.style = subtest.style;
+      await waitForFrame();
+
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        subtest.expected);
+      animation.effect.target.style = '';
+      await waitForFrame();
+
+      assert_all_properties_running_on_compositor(
+        animation.effect.getProperties(),
+        subtest.expected);
+    }, subtest.desc);
+  });
+}
+
+// Performance warning tests that set and clear the id property
+function testIdChanges() {
+  [
+    {
+      desc: 'moz-element referencing a transform',
+      frames: {
+        transform: ['translate(0px)', 'translate(100px)']
+      },
+      id: 'transformed',
+      createelement: 'width:100px; height:100px; background: -moz-element(#transformed)',
+      expected: [
+        {
+          property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningHasRenderingObserver'
+        }
+      ]
+    },
+    {
+      desc: 'moz-element referencing a translate',
+      frames: {
+        translate: ['0px', '100px']
+      },
+      id: 'transformed',
+      createelement: 'width:100px; height:100px; background: -moz-element(#transformed)',
+      expected: [
+        {
+          property: 'translate',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningHasRenderingObserver'
+        }
+      ]
+    },
+    {
+      desc: 'moz-element referencing a translate and transform',
+      frames: {
+        transform: ['translate(0px)', 'translate(100px)'],
+        translate: ['0px', '100px']
+      },
+      id: 'transformed',
+      createelement: 'width:100px; height:100px; background: -moz-element(#transformed)',
+      expected: [
+        {
+          property: 'translate',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningHasRenderingObserver'
+        },
+        {
+          property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningHasRenderingObserver'
+        }
+      ]
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      if (subtest.createelement) {
+        addDiv(t, { style: subtest.createelement });
+      }
+
+      var animation = addDivAndAnimate(t, { class: 'compositable' },
+                                       subtest.frames, 100 * MS_PER_SEC);
+      await waitForPaints();
+
+      assert_all_properties_running_on_compositor(
+        animation.effect.getProperties(),
+        subtest.expected);
+      animation.effect.target.id = subtest.id;
+      await waitForFrame();
+
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        subtest.expected);
+      animation.effect.target.id = '';
+      await waitForFrame();
+
+      assert_all_properties_running_on_compositor(
+        animation.effect.getProperties(),
+        subtest.expected);
+    }, subtest.desc);
+  });
+}
+
+function testMultipleAnimations() {
+  [
+    {
+      desc: 'opacity and transform-like properties with preserve-3d',
+      style: 'transform-style: preserve-3d',
+      animations: [
+        {
+          frames: {
+            transform: ['translate(0px)', 'translate(100px)']
+          },
+          expected: [
+            {
+              property: 'transform',
+              runningOnCompositor: true,
+            }
+          ]
+        },
+        {
+          frames: {
+            translate: ['0px', '100px']
+          },
+          expected: [
+            {
+              property: 'translate',
+              runningOnCompositor: true,
+            }
+          ]
+        },
+        {
+          frames: {
+            opacity: [0, 1]
+          },
+          expected: [
+            {
+              property: 'opacity',
+              runningOnCompositor: true,
+            }
+          ]
+        }
+      ],
+    },
+    {
+      desc: 'opacity and transform-like properties with ' +
+            'backface-visibility:hidden',
+      style: 'backface-visibility: hidden;',
+      animations: [
+        {
+          frames: {
+            transform: ['translate(0px)', 'translate(100px)']
+          },
+          expected: [
+            {
+              property: 'transform',
+              runningOnCompositor: false,
+              warning: 'CompositorAnimationWarningTransformBackfaceVisibilityHidden'
+            }
+          ]
+        },
+        {
+          frames: {
+            translate: ['0px', '100px']
+          },
+          expected: [
+            {
+              property: 'translate',
+              runningOnCompositor: false,
+              warning: 'CompositorAnimationWarningTransformBackfaceVisibilityHidden'
+            }
+          ]
+        },
+        {
+          frames: {
+            opacity: [0, 1]
+          },
+          expected: [
+            {
+              property: 'opacity',
+              runningOnCompositor: true,
+            }
+          ]
+        }
+      ],
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      var div = addDiv(t, { class: 'compositable' });
+      var animations = subtest.animations.map(anim => {
+        var animation = div.animate(anim.frames, 100 * MS_PER_SEC);
+
+        // Bind expected values to animation object.
+        animation.expected = anim.expected;
+        return animation;
+      });
+      await waitForPaints();
+
+      animations.forEach(anim => {
+        assert_all_properties_running_on_compositor(
+          anim.effect.getProperties(),
+          anim.expected);
+      });
+      div.style = subtest.style;
+      await waitForFrame();
+
+      animations.forEach(anim => {
+        assert_animation_property_state_equals(
+          anim.effect.getProperties(),
+          anim.expected);
+      });
+      div.style = '';
+      await waitForFrame();
+
+      animations.forEach(anim => {
+        assert_all_properties_running_on_compositor(
+          anim.effect.getProperties(),
+          anim.expected);
+      });
+    }, 'Multiple animations: ' + subtest.desc);
+  });
+}
+
+// Test adding/removing a 'width' keyframe on the same animation object, where
+// multiple animation objects belong to the same element.
+// The 'width' property is added to animations[1].
+function testMultipleAnimationsWithGeometricKeyframes() {
+  [
+    {
+      desc: 'transform and opacity with geometric keyframes',
+      animations: [
+        {
+          frames: {
+            transform: ['translate(0px)', 'translate(100px)']
+          },
+          expected: {
+            withoutGeometric: [
+              {
+                property: 'transform',
+                runningOnCompositor: true
+              }
+            ],
+            withGeometric: [
+              {
+                property: 'transform',
+                runningOnCompositor: false,
+                warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+              }
+            ]
+          }
+        },
+        {
+          frames: {
+            opacity: [0, 1]
+          },
+          expected: {
+            withoutGeometric: [
+              {
+                property: 'opacity',
+                runningOnCompositor: true,
+              }
+            ],
+            withGeometric: [
+              {
+                property: 'width',
+                runningOnCompositor: false,
+              },
+              {
+                property: 'opacity',
+                runningOnCompositor: true,
+              }
+            ]
+          }
+        }
+      ],
+    },
+    {
+      desc: 'opacity and transform with geometric keyframes',
+      animations: [
+        {
+          frames: {
+            opacity: [0, 1]
+          },
+          expected: {
+            withoutGeometric: [
+              {
+                property: 'opacity',
+                runningOnCompositor: true,
+              }
+            ],
+            withGeometric: [
+              {
+                property: 'opacity',
+                runningOnCompositor: true,
+              }
+            ]
+          }
+        },
+        {
+          frames: {
+            transform: ['translate(0px)', 'translate(100px)']
+          },
+          expected: {
+            withoutGeometric: [
+              {
+                property: 'transform',
+                runningOnCompositor: true
+              }
+            ],
+            withGeometric: [
+              {
+                property: 'width',
+                runningOnCompositor: false,
+              },
+              {
+                property: 'transform',
+                runningOnCompositor: false,
+                warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+              }
+            ]
+          }
+        }
+      ]
+    },
+    {
+      desc: 'opacity and translate with geometric keyframes',
+      animations: [
+        {
+          frames: {
+            opacity: [0, 1]
+          },
+          expected: {
+            withoutGeometric: [
+              {
+                property: 'opacity',
+                runningOnCompositor: true,
+              }
+            ],
+            withGeometric: [
+              {
+                property: 'opacity',
+                runningOnCompositor: true,
+              }
+            ]
+          }
+        },
+        {
+          frames: {
+            translate: ['0px', '100px']
+          },
+          expected: {
+            withoutGeometric: [
+              {
+                property: 'translate',
+                runningOnCompositor: true
+              }
+            ],
+            withGeometric: [
+              {
+                property: 'width',
+                runningOnCompositor: false,
+              },
+              {
+                property: 'translate',
+                runningOnCompositor: false,
+                warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+              }
+            ]
+          }
+        }
+      ]
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      var div = addDiv(t, { class: 'compositable' });
+      var animations = subtest.animations.map(anim => {
+        var animation = div.animate(anim.frames, 100 * MS_PER_SEC);
+
+        // Bind expected values to animation object.
+        animation.expected = anim.expected;
+        return animation;
+      });
+      await waitForPaints();
+      // First, all animations are running on compositor.
+      animations.forEach(anim => {
+        assert_animation_property_state_equals(
+          anim.effect.getProperties(),
+          anim.expected.withoutGeometric);
+      });
+
+      // Add a 'width' property to animations[1].
+      var keyframes = animations[1].effect.getKeyframes();
+
+      keyframes[0].width = '100px';
+      keyframes[1].width = '200px';
+
+      animations[1].effect.setKeyframes(keyframes);
+      await waitForFrame();
+
+      // Now the transform animation is not running on compositor because of
+      // the 'width' property.
+      animations.forEach(anim => {
+        assert_animation_property_state_equals(
+          anim.effect.getProperties(),
+          anim.expected.withGeometric);
+      });
+
+      // Remove the 'width' property from animations[1].
+      var keyframes = animations[1].effect.getKeyframes();
+
+      delete keyframes[0].width;
+      delete keyframes[1].width;
+
+      animations[1].effect.setKeyframes(keyframes);
+      await waitForFrame();
+
+      // Finally, all animations are running on compositor.
+      animations.forEach(anim => {
+        assert_animation_property_state_equals(
+          anim.effect.getProperties(),
+          anim.expected.withoutGeometric);
+      });
+    }, 'Multiple animations with geometric property: ' + subtest.desc);
+  });
+}
+
+// Tests adding/removing 'width' animation on the same element which has async
+// animations.
+function testMultipleAnimationsWithGeometricAnimations() {
+  [
+    {
+      desc: 'transform',
+      animations: [
+        {
+          frames: {
+            transform: ['translate(0px)', 'translate(100px)']
+          },
+          expected: [
+            {
+              property: 'transform',
+              runningOnCompositor: false,
+              warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+            }
+          ]
+        },
+      ]
+    },
+    {
+      desc: 'translate',
+      animations: [
+        {
+          frames: {
+            translate: ['0px', '100px']
+          },
+          expected: [
+            {
+              property: 'translate',
+              runningOnCompositor: false,
+              warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+            }
+          ]
+        },
+      ]
+    },
+    {
+      desc: 'opacity',
+      animations: [
+        {
+          frames: {
+            opacity: [0, 1]
+          },
+          expected: [
+            {
+              property: 'opacity',
+              runningOnCompositor: true
+            }
+          ]
+        },
+      ]
+    },
+    {
+      desc: 'opacity, transform, and translate',
+      animations: [
+        {
+          frames: {
+            transform: ['translate(0px)', 'translate(100px)']
+          },
+          expected: [
+            {
+              property: 'transform',
+              runningOnCompositor: false,
+              warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+            }
+          ]
+        },
+        {
+          frames: {
+            translate: ['0px', '100px']
+          },
+          expected: [
+            {
+              property: 'translate',
+              runningOnCompositor: false,
+              warning: 'CompositorAnimationWarningTransformWithGeometricProperties'
+            }
+          ]
+        },
+        {
+          frames: {
+            opacity: [0, 1]
+          },
+          expected: [
+            {
+              property: 'opacity',
+              runningOnCompositor: true,
+            }
+          ]
+        }
+      ],
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      var div = addDiv(t, { class: 'compositable' });
+      var animations = subtest.animations.map(anim => {
+        var animation = div.animate(anim.frames, 100 * MS_PER_SEC);
+
+        // Bind expected values to animation object.
+        animation.expected = anim.expected;
+        return animation;
+      });
+
+      var widthAnimation;
+
+      await waitForPaints();
+      animations.forEach(anim => {
+        assert_all_properties_running_on_compositor(
+          anim.effect.getProperties(),
+          anim.expected);
+      });
+
+      // Append 'width' animation on the same element.
+      widthAnimation = div.animate({ width: ['100px', '200px'] },
+                                   100 * MS_PER_SEC);
+      await waitForFrame();
+
+      // Now transform animations are not running on compositor because of
+      // the 'width' animation.
+      animations.forEach(anim => {
+        assert_animation_property_state_equals(
+          anim.effect.getProperties(),
+          anim.expected);
+      });
+      // Remove the 'width' animation.
+      widthAnimation.cancel();
+      await waitForFrame();
+
+      // Now all animations are running on compositor.
+      animations.forEach(anim => {
+        assert_all_properties_running_on_compositor(
+          anim.effect.getProperties(),
+          anim.expected);
+      });
+    }, 'Multiple async animations and geometric animation: ' + subtest.desc);
+  });
+}
+
+function testSmallElements() {
+  [
+    {
+      desc: 'opacity on small element',
+      frames: {
+        opacity: [0, 1]
+      },
+      style: { style: 'width: 8px; height: 8px; background-color: red;' +
+                      // We need to set transform here to try creating an
+                      // individual frame for this opacity element.
+                      // Without this, this small element is created on the same
+                      // nsIFrame of mochitest iframe, i.e. the document which are
+                      // running this test, as a result the layer corresponding
+                      // to the frame is sent to compositor.
+                      'transform: translateX(100px);' },
+      expected: [
+        {
+          property: 'opacity',
+          runningOnCompositor: true
+        }
+      ]
+    },
+    {
+      desc: 'transform on small element',
+      frames: {
+        transform: ['translate(0px)', 'translate(100px)']
+      },
+      style: { style: 'width: 8px; height: 8px; background-color: red;' },
+      expected: [
+        {
+          property: 'transform',
+          runningOnCompositor: true
+        }
+      ]
+    },
+    {
+      desc: 'translate on small element',
+      frames: {
+        translate: ['0px', '100px']
+      },
+      style: { style: 'width: 8px; height: 8px; background-color: red;' },
+      expected: [
+        {
+          property: 'translate',
+          runningOnCompositor: true
+        }
+      ]
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+    var div = addDiv(t, subtest.style);
+    var animation = div.animate(subtest.frames, 100 * MS_PER_SEC);
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animation.effect.getProperties(),
+      subtest.expected);
+    }, subtest.desc);
+  });
+}
+
+function testSynchronizedAnimations() {
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ] },
+                                100 * MS_PER_SEC);
+    const animB = elemB.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+      } ]);
+  }, 'Animations created within the same tick are synchronized'
+     + ' (compositor animation created first)');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+    const elemC = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ] },
+                                100 * MS_PER_SEC);
+    const animB = elemB.animate({ translate: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+    const animC = elemC.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [
+        { property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+      } ]);
+    assert_animation_property_state_equals(
+      animB.effect.getProperties(),
+      [
+        { property: 'translate',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+      } ]);
+  }, 'Animations created within the same tick are synchronized'
+     + ' (compositor animation created first/second)');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+    const elemC = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+    const animB = elemB.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ] },
+                                100 * MS_PER_SEC);
+    const animC = elemC.animate({ translate: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animB.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+      } ]);
+    assert_animation_property_state_equals(
+      animC.effect.getProperties(),
+      [
+        { property: 'translate',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+      } ]);
+  }, 'Animations created within the same tick are synchronized'
+     + ' (compositor animation created second/third)');
+
+  promise_test(async t => {
+    const attrs = { class: 'compositable',
+                    style: 'transition: all 100s' };
+    const elemA = addDiv(t, attrs);
+    const elemB = addDiv(t, attrs);
+    elemA.style.transform = 'translate(0px)';
+    elemB.style.marginLeft = '0px';
+    getComputedStyle(elemA).transform;
+    getComputedStyle(elemB).marginLeft;
+
+    // Generally the sequence of steps is as follows:
+    //
+    //   Tick -> requestAnimationFrame -> Style -> Paint -> Events (-> Tick...)
+    //
+    // In this test we want to set up two transitions during the "Events"
+    // stage but only flush style for one such that the second one is actually
+    // generated during the "Style" stage of the *next* tick.
+    //
+    // Web content often generates transitions in this way (that is, it doesn't
+    // pay regard to when style is flushed and nor should it). However, we
+    // still want transitions generated in this way to be synchronized.
+    let timeForFirstFrame;
+    await waitForIdle();
+
+    timeForFirstFrame = document.timeline.currentTime;
+    elemA.style.transform = 'translate(100px)';
+    // Flush style to trigger first transition
+    getComputedStyle(elemA).transform;
+    elemB.style.marginLeft = '100px';
+    // DON'T flush style here (this includes calling getAnimations!)
+    await waitForFrame();
+
+    assert_not_equals(timeForFirstFrame, document.timeline.currentTime,
+                      'Should be on the other side of a tick');
+    // Wait another tick so we can let the transition be started
+    // by regular style resolution.
+    await waitForFrame();
+
+    const transitionA = elemA.getAnimations()[0];
+    assert_animation_property_state_equals(
+      transitionA.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+      } ]);
+  }, 'Transitions created before and after a tick are synchronized');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ],
+                                  opacity: [ 0, 1 ] },
+                                100 * MS_PER_SEC);
+    const animB = elemB.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+        },
+        { property: 'opacity',
+          runningOnCompositor: true
+        } ]);
+  }, 'Opacity animations on the same element continue running on the'
+     + ' compositor when transform animations are synchronized with geometric'
+     + ' animations');
+
+  promise_test(async t => {
+    const transitionElem = addDiv(t, {
+      style: 'margin-left: 0px; transition: margin-left 100s',
+    });
+    getComputedStyle(transitionElem).marginLeft;
+
+    await waitForFrame();
+
+    transitionElem.style.marginLeft = '100px';
+    const cssTransition = transitionElem.getAnimations()[0];
+
+    const animationElem = addDiv(t, {
+      class: 'compositable',
+      style: 'animation: translate 100s',
+    });
+    const cssAnimation = animationElem.getAnimations()[0];
+
+    await Promise.all([cssTransition.ready, cssAnimation.ready]);
+
+    assert_animation_property_state_equals(cssAnimation.effect.getProperties(),
+      [{ property: 'transform',
+         runningOnCompositor: true }]);
+  }, 'CSS Animations are NOT synchronized with CSS Transitions');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+    await waitForPaints();
+
+    let animB = elemB.animate({ transform: [ 'translate(0px)',
+                                             'translate(100px)' ] },
+                              100 * MS_PER_SEC);
+    await animB.ready;
+
+    assert_animation_property_state_equals(
+      animB.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: true } ]);
+  }, 'Transform animations are NOT synchronized with geometric animations'
+     + ' started in the previous frame');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ] },
+                                100 * MS_PER_SEC);
+    await waitForPaints();
+
+    let animB = elemB.animate({ marginLeft: [ '0px', '100px' ] },
+                              100 * MS_PER_SEC);
+    await animB.ready;
+
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: true } ]);
+  }, 'Transform animations are NOT synchronized with geometric animations'
+     + ' started in the next frame');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ] },
+                                100 * MS_PER_SEC);
+    const animB = elemB.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+    animB.pause();
+
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [ { property: 'transform', runningOnCompositor: true } ]);
+  }, 'Paused animations are not synchronized');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ] },
+                                100 * MS_PER_SEC);
+    const animB = elemB.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+
+    // Seek one of the animations so that their start times will differ
+    animA.currentTime = 5000;
+
+    await waitForPaints();
+
+    assert_not_equals(animA.startTime, animB.startTime,
+                      'Animations should have different start times');
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformWithSyncGeometricAnimations'
+      } ]);
+  }, 'Animations are synchronized based on when they are started'
+     + ' and NOT their start time');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ] },
+                                100 * MS_PER_SEC);
+    const animB = elemB.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: false } ]);
+    // Restart animation
+    animA.pause();
+    animA.play();
+    await animA.ready;
+
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: true } ]);
+  }, 'An initially synchronized animation may be unsynchronized if restarted');
+
+  promise_test(async t => {
+    const elemA = addDiv(t, { class: 'compositable' });
+    const elemB = addDiv(t, { class: 'compositable' });
+
+    const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                               'translate(100px)' ] },
+                                100 * MS_PER_SEC);
+    const animB = elemB.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+
+    // Clear target effect
+    animB.effect.target = null;
+
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animA.effect.getProperties(),
+      [ { property: 'transform',
+          runningOnCompositor: true } ]);
+  }, 'A geometric animation with no target element is not synchronized');
+}
+
+function testTooLargeFrame() {
+  [
+    {
+      property: 'transform',
+      frames: { transform: ['translate(0px)', 'translate(100px)'] },
+    },
+    {
+      property: 'translate',
+      frames: { translate: ['0px', '100px'] },
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      var animation = addDivAndAnimate(t,
+                                       { class: 'compositable' },
+                                       subtest.frames,
+                                       100 * MS_PER_SEC);
+      await waitForPaints();
+
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ { property: subtest.property, runningOnCompositor: true } ]);
+      animation.effect.target.style = 'width: 10000px; height: 10000px';
+      await waitForFrame();
+
+      // viewport depends on test environment.
+      var expectedWarning = new RegExp(
+        "Animation cannot be run on the compositor because the area of the frame " +
+        "\\(\\d+\\) is too large relative to the viewport " +
+        "\\(larger than \\d+\\)");
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ {
+          property: subtest.property,
+          runningOnCompositor: false,
+          warning: expectedWarning
+        } ]);
+      animation.effect.target.style = 'width: 100px; height: 100px';
+      await waitForFrame();
+
+      // With WebRender we appear to stick to the previous layerization decision
+      // after changing the bounds back to a smaller object.
+      const isWebRender =
+        SpecialPowers.DOMWindowUtils.layerManagerType.startsWith('WebRender');
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ { property: subtest.property, runningOnCompositor: !isWebRender } ]);
+    }, subtest.property + ' on too big element - area');
+
+    promise_test(async t => {
+      var animation = addDivAndAnimate(t,
+                                       { class: 'compositable' },
+                                       subtest.frames,
+                                       100 * MS_PER_SEC);
+      await waitForPaints();
+
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ { property: subtest.property, runningOnCompositor: true } ]);
+      animation.effect.target.style = 'width: 20000px; height: 1px';
+      await waitForFrame();
+
+      // viewport depends on test environment.
+      var expectedWarning = new RegExp(
+        "Animation cannot be run on the compositor because the frame size " +
+        "\\(20000, 1\\) is too large relative to the viewport " +
+        "\\(larger than \\(\\d+, \\d+\\)\\) or larger than the " +
+        "maximum allowed value \\(\\d+, \\d+\\)");
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ {
+          property: subtest.property,
+          runningOnCompositor: false,
+          warning: expectedWarning
+        } ]);
+      animation.effect.target.style = 'width: 100px; height: 100px';
+      await waitForFrame();
+
+      const isWebRender =
+        SpecialPowers.DOMWindowUtils.layerManagerType.startsWith('WebRender');
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ { property: subtest.property, runningOnCompositor: !isWebRender } ]);
+    }, subtest.property + ' on too big element - dimensions');
+  });
+}
+
+function testTransformSVG() {
+  [
+    {
+      property: 'transform',
+      frames: { transform: ['translate(0px)', 'translate(100px)'] },
+    },
+    {
+      property: 'translate',
+      frames: { translate: ['0px', '100px'] },
+    },
+    {
+      property: 'rotate',
+      frames: { rotate: ['0deg', '45deg'] },
+    },
+    {
+      property: 'scale',
+      frames: { scale: ['1', '2'] },
+    },
+  ].forEach(subtest => {
+    promise_test(async t => {
+      var svg  = document.createElementNS('http://www.w3.org/2000/svg', 'svg');
+      svg.setAttribute('width', '100');
+      svg.setAttribute('height', '100');
+      var rect = document.createElementNS('http://www.w3.org/2000/svg', 'rect');
+      rect.setAttribute('width', '100');
+      rect.setAttribute('height', '100');
+      rect.setAttribute('fill', 'red');
+      svg.appendChild(rect);
+      document.body.appendChild(svg);
+      t.add_cleanup(() => {
+        svg.remove();
+      });
+
+      var animation = svg.animate(subtest.frames, 100 * MS_PER_SEC);
+      await waitForPaints();
+
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ { property: subtest.property, runningOnCompositor: true } ]);
+      svg.setAttribute('transform', 'translate(10, 20)');
+      await waitForFrame();
+
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ {
+          property: subtest.property,
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningTransformSVG'
+        } ]);
+      svg.removeAttribute('transform');
+      await waitForFrame();
+
+      assert_animation_property_state_equals(
+        animation.effect.getProperties(),
+        [ { property: subtest.property, runningOnCompositor: true } ]);
+    }, subtest.property + ' of nsIFrame with SVG transform');
+  });
+}
+
+function testImportantRuleOverride() {
+  promise_test(async t => {
+    const elem = addDiv(t, { class: 'compositable' });
+    const anim = elem.animate({ translate: [ '0px', '100px' ],
+                                rotate: ['0deg', '90deg'] },
+                                100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(anim);
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      anim.effect.getProperties(),
+      [ { property: 'translate', runningOnCompositor: true },
+        { property: 'rotate', runningOnCompositor: true } ]
+    );
+
+    elem.style.setProperty('rotate', '45deg', 'important');
+    getComputedStyle(elem).rotate;
+
+    await waitForFrame();
+
+    assert_animation_property_state_equals(
+      anim.effect.getProperties(),
+      [
+        {
+          property: 'translate',
+          runningOnCompositor: false,
+          warning:
+            'CompositorAnimationWarningTransformIsBlockedByImportantRules'
+        },
+        {
+          property: 'rotate',
+          runningOnCompositor: false,
+          warning:
+            'CompositorAnimationWarningTransformIsBlockedByImportantRules'
+        },
+      ]
+    );
+  }, 'The animations of transform-like properties are not running on the ' +
+     'compositor because any of the properties has important rules');
+}
+
+function testCurrentColor() {
+  if (SpecialPowers.DOMWindowUtils.layerManagerType.startsWith('WebRender')) {
+    return; // skip this test until bug 1510030 landed.
+  }
+  promise_test(async t => {
+    const animation = addDivAndAnimate(t, { class: 'compositable' },
+                                       { backgroundColor: [ 'currentColor',
+                                                            'red' ] },
+                                       100 * MS_PER_SEC);
+    await waitForPaints();
+
+    assert_animation_property_state_equals(
+      animation.effect.getProperties(),
+      [ { property: 'background-color',
+          runningOnCompositor: false,
+          warning: 'CompositorAnimationWarningHasCurrentColor'
+      } ]);
+  }, 'Background color animations with `current-color` don\'t run on the '
+     + 'compositor');
+}
+
+function start() {
+  var bundleService = SpecialPowers.Cc['@mozilla.org/intl/stringbundle;1']
+    .getService(SpecialPowers.Ci.nsIStringBundleService);
+  gStringBundle = bundleService
+    .createBundle("chrome://global/locale/layout_errors.properties");
+
+  testBasicOperation();
+  testKeyframesWithGeometricProperties();
+  testSetOfGeometricProperties();
+  testStyleChanges();
+  testIdChanges();
+  testMultipleAnimations();
+  testMultipleAnimationsWithGeometricKeyframes();
+  testMultipleAnimationsWithGeometricAnimations();
+  testSmallElements();
+  testSynchronizedAnimations();
+  testTooLargeFrame();
+  testTransformSVG();
+  testImportantRuleOverride();
+  testCurrentColor();
+
+  promise_test(async t => {
+    var div = addDiv(t, { class: 'compositable',
+                          style: 'animation: fade 100s' });
+    var cssAnimation = div.getAnimations()[0];
+    var scriptAnimation = div.animate({ opacity: [ 1, 0 ] }, 100 * MS_PER_SEC);
+
+    await waitForPaints();
+    assert_animation_property_state_equals(
+      cssAnimation.effect.getProperties(),
+      [ { property: 'opacity', runningOnCompositor: true } ]);
+    assert_animation_property_state_equals(
+      scriptAnimation.effect.getProperties(),
+      [ { property: 'opacity', runningOnCompositor: true } ]);
+  }, 'overridden animation');
+
+  done();
+}
+
+</script>
+
+</body>
diff --git a/dom/animation/test/chrome/test_animation_properties.html b/dom/animation/test/chrome/test_animation_properties.html
new file mode 100644
index 0000000000..b9d6dcbef1
--- /dev/null
+++ b/dom/animation/test/chrome/test_animation_properties.html
@@ -0,0 +1,838 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Bug 1254419 - Test the values returned by
+       KeyframeEffect.getProperties()</title>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+</head>
+<body>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1254419"
+  target="_blank">Mozilla Bug 1254419</a>
+<div id="log"></div>
+<style>
+
+:root {
+  --var-100px: 100px;
+  --var-100px-200px: 100px 200px;
+}
+div {
+  font-size: 10px; /* For calculating em-based units */
+}
+</style>
+<script>
+'use strict';
+
+var gTests = [
+
+  // ---------------------------------------------------------------------
+  //
+  // Tests for property-indexed specifications
+  //
+  // ---------------------------------------------------------------------
+
+  { desc:     'a one-property two-value property-indexed specification',
+    frames:   { left: ['10px', '20px'] },
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '20px', 'replace') ] } ]
+  },
+  { desc:     'a one-shorthand-property two-value property-indexed'
+              + ' specification',
+    frames:   { margin: ['10px', '10px 20px 30px 40px'] },
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '10px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '20px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '40px', 'replace') ] } ]
+  },
+  { desc:     'a two-property (one shorthand and one of its longhand'
+              + ' components) two-value property-indexed specification',
+    frames:   { marginTop: ['50px', '60px'],
+                margin: ['10px', '10px 20px 30px 40px'] },
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, '50px', 'replace', 'linear'),
+                            valueFormat(1, '60px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '20px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '40px', 'replace') ] } ]
+  },
+  { desc:     'a two-property property-indexed specification with different'
+              + ' numbers of values',
+    frames:   { left: ['10px', '20px', '30px'],
+                top: ['40px', '50px'] },
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(0.5, '20px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'top',
+                  values: [ valueFormat(0, '40px', 'replace', 'linear'),
+                            valueFormat(1, '50px', 'replace') ] } ]
+  },
+  { desc:     'a property-indexed specification with an invalid value',
+    frames:   { left: ['10px', '20px', '30px', '40px', '50px'],
+                top:  ['15px', '25px', 'invalid', '45px', '55px'] },
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(0.25, '20px', 'replace', 'linear'),
+                            valueFormat(0.5, '30px', 'replace', 'linear'),
+                            valueFormat(0.75, '40px', 'replace', 'linear'),
+                            valueFormat(1, '50px', 'replace') ] },
+                { property: 'top',
+                  values: [ valueFormat(0, '15px', 'replace', 'linear'),
+                            valueFormat(0.25, '25px', 'replace', 'linear'),
+                            valueFormat(0.75, '45px', 'replace', 'linear'),
+                            valueFormat(1, '55px', 'replace') ] } ]
+  },
+  { desc:     'a one-property two-value property-indexed specification that'
+              + ' needs to stringify its values',
+    frames:   { opacity: [0, 1] },
+    expected: [ { property: 'opacity',
+                  values: [ valueFormat(0, '0', 'replace', 'linear'),
+                            valueFormat(1, '1', 'replace') ] } ]
+  },
+  { desc:     'a property-indexed keyframe where a lesser shorthand precedes'
+              + ' a greater shorthand',
+    frames:   { borderLeft: [ '1px solid rgb(1, 2, 3)',
+                              '2px solid rgb(4, 5, 6)' ],
+                border:     [ '3px dotted rgb(7, 8, 9)',
+                              '4px dashed rgb(10, 11, 12)' ] },
+    expected: [ { property: 'border-bottom-color',
+                  values: [ valueFormat(0, 'rgb(7, 8, 9)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(10, 11, 12)', 'replace') ] },
+                { property: 'border-left-color',
+                  values: [ valueFormat(0, 'rgb(1, 2, 3)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(4, 5, 6)', 'replace') ] },
+                { property: 'border-right-color',
+                  values: [ valueFormat(0, 'rgb(7, 8, 9)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(10, 11, 12)', 'replace') ] },
+                { property: 'border-top-color',
+                  values: [ valueFormat(0, 'rgb(7, 8, 9)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(10, 11, 12)', 'replace') ] },
+                { property: 'border-bottom-width',
+                  values: [ valueFormat(0, '3px', 'replace', 'linear'),
+                            valueFormat(1, '4px', 'replace') ] },
+                { property: 'border-left-width',
+                  values: [ valueFormat(0, '1px', 'replace', 'linear'),
+                            valueFormat(1, '2px', 'replace') ] },
+                { property: 'border-right-width',
+                  values: [ valueFormat(0, '3px', 'replace', 'linear'),
+                            valueFormat(1, '4px', 'replace') ] },
+                { property: 'border-top-width',
+                  values: [ valueFormat(0, '3px', 'replace', 'linear'),
+                            valueFormat(1, '4px', 'replace') ] },
+                { property: 'border-bottom-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-left-style',
+                  values: [ valueFormat(0, 'solid', 'replace', 'linear'),
+                            valueFormat(1, 'solid', 'replace') ] },
+                { property: 'border-right-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-top-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-image-outset',
+                  values: [ valueFormat(0, '0', 'replace', 'linear'),
+                            valueFormat(1, '0', 'replace') ] },
+                { property: 'border-image-repeat',
+                  values: [ valueFormat(0, 'stretch', 'replace', 'linear'),
+                            valueFormat(1, 'stretch', 'replace') ] },
+                { property: 'border-image-slice',
+                  values: [ valueFormat(0, '100%', 'replace', 'linear'),
+                            valueFormat(1, '100%', 'replace') ] },
+                { property: 'border-image-source',
+                  values: [ valueFormat(0, 'none', 'replace', 'linear'),
+                            valueFormat(1, 'none', 'replace') ] },
+                { property: 'border-image-width',
+                  values: [ valueFormat(0, '1', 'replace', 'linear'),
+                            valueFormat(1, '1', 'replace') ] },
+    ]
+  },
+  { desc:     'a property-indexed keyframe where a greater shorthand precedes'
+              + ' a lesser shorthand',
+    frames:   { border:     [ '3px dotted rgb(7, 8, 9)',
+                              '4px dashed rgb(10, 11, 12)' ],
+                borderLeft: [ '1px solid rgb(1, 2, 3)',
+                              '2px solid rgb(4, 5, 6)' ] },
+    expected: [ { property: 'border-bottom-color',
+                  values: [ valueFormat(0, 'rgb(7, 8, 9)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(10, 11, 12)', 'replace') ] },
+                { property: 'border-left-color',
+                  values: [ valueFormat(0, 'rgb(1, 2, 3)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(4, 5, 6)', 'replace') ] },
+                { property: 'border-right-color',
+                  values: [ valueFormat(0, 'rgb(7, 8, 9)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(10, 11, 12)', 'replace') ] },
+                { property: 'border-top-color',
+                  values: [ valueFormat(0, 'rgb(7, 8, 9)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(10, 11, 12)', 'replace') ] },
+                { property: 'border-bottom-width',
+                  values: [ valueFormat(0, '3px', 'replace', 'linear'),
+                            valueFormat(1, '4px', 'replace') ] },
+                { property: 'border-left-width',
+                  values: [ valueFormat(0, '1px', 'replace', 'linear'),
+                            valueFormat(1, '2px', 'replace') ] },
+                { property: 'border-right-width',
+                  values: [ valueFormat(0, '3px', 'replace', 'linear'),
+                            valueFormat(1, '4px', 'replace') ] },
+                { property: 'border-top-width',
+                  values: [ valueFormat(0, '3px', 'replace', 'linear'),
+                            valueFormat(1, '4px', 'replace') ] },
+                { property: 'border-bottom-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-left-style',
+                  values: [ valueFormat(0, 'solid', 'replace', 'linear'),
+                            valueFormat(1, 'solid', 'replace') ] },
+                { property: 'border-right-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-top-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-image-outset',
+                  values: [ valueFormat(0, '0', 'replace', 'linear'),
+                            valueFormat(1, '0', 'replace') ] },
+                { property: 'border-image-repeat',
+                  values: [ valueFormat(0, 'stretch', 'replace', 'linear'),
+                            valueFormat(1, 'stretch', 'replace') ] },
+                { property: 'border-image-slice',
+                  values: [ valueFormat(0, '100%', 'replace', 'linear'),
+                            valueFormat(1, '100%', 'replace') ] },
+                { property: 'border-image-source',
+                  values: [ valueFormat(0, 'none', 'replace', 'linear'),
+                            valueFormat(1, 'none', 'replace') ] },
+                { property: 'border-image-width',
+                  values: [ valueFormat(0, '1', 'replace', 'linear'),
+                            valueFormat(1, '1', 'replace') ] },
+    ]
+  },
+
+  // ---------------------------------------------------------------------
+  //
+  // Tests for keyframe sequences
+  //
+  // ---------------------------------------------------------------------
+
+  { desc:     'a keyframe sequence specification with repeated values at'
+              + ' offset 0/1 with different easings',
+    frames:   [ { offset: 0.0, left: '100px', easing: 'ease' },
+                { offset: 0.0, left: '200px', easing: 'ease' },
+                { offset: 0.5, left: '300px', easing: 'linear' },
+                { offset: 1.0, left: '400px', easing: 'ease-out' },
+                { offset: 1.0, left: '500px', easing: 'step-end' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '100px', 'replace'),
+                            valueFormat(0, '200px', 'replace', 'ease'),
+                            valueFormat(0.5, '300px', 'replace', 'linear'),
+                            valueFormat(1, '400px', 'replace'),
+                            valueFormat(1, '500px', 'replace') ] } ]
+  },
+  { desc:     'a one-property two-keyframe sequence',
+    frames:   [ { offset: 0, left: '10px' },
+                { offset: 1, left: '20px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '20px', 'replace') ] } ]
+  },
+  { desc:     'a two-property two-keyframe sequence',
+    frames:   [ { offset: 0, left: '10px', top: '30px' },
+                { offset: 1, left: '20px', top: '40px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '20px', 'replace') ] },
+                { property: 'top',
+                  values: [ valueFormat(0, '30px', 'replace', 'linear'),
+                            valueFormat(1, '40px', 'replace') ] } ]
+  },
+  { desc:     'a one shorthand property two-keyframe sequence',
+    frames:   [ { offset: 0, margin: '10px' },
+                { offset: 1, margin: '20px 30px 40px 50px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '20px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '40px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '50px', 'replace') ] } ]
+  },
+  { desc:     'a two-property (a shorthand and one of its component longhands)'
+              + ' two-keyframe sequence',
+    frames:   [ { offset: 0, margin: '10px', marginTop: '20px' },
+                { offset: 1, marginTop: '70px',
+                             margin: '30px 40px 50px 60px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, '20px', 'replace', 'linear'),
+                            valueFormat(1, '70px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '40px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '50px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '60px', 'replace') ] } ]
+  },
+  { desc:     'a keyframe sequence with duplicate values for a given interior'
+              + ' offset',
+    frames:   [ { offset: 0.0, left: '10px' },
+                { offset: 0.5, left: '20px' },
+                { offset: 0.5, left: '30px' },
+                { offset: 0.5, left: '40px' },
+                { offset: 1.0, left: '50px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(0.5, '20px', 'replace'),
+                            valueFormat(0.5, '40px', 'replace', 'linear'),
+                            valueFormat(1, '50px', 'replace') ] } ]
+  },
+  { desc:     'a keyframe sequence with duplicate values for offsets 0 and 1',
+    frames:   [ { offset: 0, left: '10px' },
+                { offset: 0, left: '20px' },
+                { offset: 0, left: '30px' },
+                { offset: 1, left: '40px' },
+                { offset: 1, left: '50px' },
+                { offset: 1, left: '60px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace'),
+                            valueFormat(0, '30px', 'replace', 'linear'),
+                            valueFormat(1, '40px', 'replace'),
+                            valueFormat(1, '60px', 'replace') ] } ]
+  },
+  { desc:     'a two-property four-keyframe sequence',
+    frames:   [ { offset: 0, left: '10px' },
+                { offset: 0, top: '20px' },
+                { offset: 1, top: '30px' },
+                { offset: 1, left: '40px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '40px', 'replace') ] },
+                { property: 'top',
+                  values: [ valueFormat(0, '20px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] } ]
+  },
+  { desc:     'a one-property keyframe sequence with some omitted offsets',
+    frames:   [ { offset: 0.00, left: '10px' },
+                { offset: 0.25, left: '20px' },
+                { left: '30px' },
+                { left: '40px' },
+                { offset: 1.00, left: '50px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(0.25, '20px', 'replace', 'linear'),
+                            valueFormat(0.5, '30px', 'replace', 'linear'),
+                            valueFormat(0.75, '40px', 'replace', 'linear'),
+                            valueFormat(1, '50px', 'replace') ] } ]
+  },
+  { desc:     'a two-property keyframe sequence with some omitted offsets',
+    frames:   [ { offset: 0.00, left: '10px', top: '20px' },
+                { offset: 0.25, left: '30px' },
+                { left: '40px' },
+                { left: '50px', top: '60px' },
+                { offset: 1.00, left: '70px', top: '80px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(0.25, '30px', 'replace', 'linear'),
+                            valueFormat(0.5, '40px', 'replace', 'linear'),
+                            valueFormat(0.75, '50px', 'replace', 'linear'),
+                            valueFormat(1, '70px', 'replace') ] },
+                { property: 'top',
+                  values: [ valueFormat(0, '20px', 'replace', 'linear'),
+                            valueFormat(0.75, '60px', 'replace', 'linear'),
+                            valueFormat(1, '80px', 'replace') ] } ]
+  },
+  { desc:     'a one-property keyframe sequence with all omitted offsets',
+    frames:   [ { left: '10px' },
+                { left: '20px' },
+                { left: '30px' },
+                { left: '40px' },
+                { left: '50px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(0.25, '20px', 'replace', 'linear'),
+                            valueFormat(0.5, '30px', 'replace', 'linear'),
+                            valueFormat(0.75, '40px', 'replace', 'linear'),
+                            valueFormat(1, '50px', 'replace') ] } ]
+  },
+  { desc:     'a keyframe sequence with different easing values, but the'
+              + ' same easing value for a given offset',
+    frames:   [ { offset: 0.0, easing: 'ease',     left: '10px'},
+                { offset: 0.0, easing: 'ease',     top: '20px'},
+                { offset: 0.5, easing: 'linear',   left: '30px' },
+                { offset: 0.5, easing: 'linear',   top: '40px' },
+                { offset: 1.0, easing: 'step-end', left: '50px' },
+                { offset: 1.0, easing: 'step-end', top: '60px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'ease'),
+                            valueFormat(0.5, '30px', 'replace', 'linear'),
+                            valueFormat(1, '50px', 'replace') ] },
+                { property: 'top',
+                  values: [ valueFormat(0, '20px', 'replace', 'ease'),
+                            valueFormat(0.5, '40px', 'replace', 'linear'),
+                            valueFormat(1, '60px', 'replace') ] } ]
+  },
+  { desc:     'a one-property two-keyframe sequence that needs to'
+              + ' stringify its values',
+    frames:   [ { offset: 0, opacity: 0 },
+                { offset: 1, opacity: 1 } ],
+    expected: [ { property: 'opacity',
+                  values: [ valueFormat(0, '0', 'replace', 'linear'),
+                            valueFormat(1, '1', 'replace') ] } ]
+  },
+  { desc:     'a keyframe sequence where shorthand precedes longhand',
+    frames:   [ { offset: 0, margin: '10px', marginRight: '20px' },
+                { offset: 1, margin: '30px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '20px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] } ]
+  },
+  { desc:     'a keyframe sequence where longhand precedes shorthand',
+    frames:   [ { offset: 0, marginRight: '20px', margin: '10px' },
+                { offset: 1, margin: '30px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '20px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '30px', 'replace') ] } ]
+  },
+  { desc:     'a keyframe sequence where lesser shorthand precedes greater'
+              + ' shorthand',
+    frames:   [ { offset: 0, borderLeft: '1px solid rgb(1, 2, 3)',
+                             border: '2px dotted rgb(4, 5, 6)' },
+                { offset: 1, border: '3px dashed rgb(7, 8, 9)' } ],
+    expected: [ { property: 'border-bottom-color',
+                  values: [ valueFormat(0, 'rgb(4, 5, 6)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(7, 8, 9)', 'replace') ] },
+                { property: 'border-left-color',
+                  values: [ valueFormat(0, 'rgb(1, 2, 3)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(7, 8, 9)', 'replace') ] },
+                { property: 'border-right-color',
+                  values: [ valueFormat(0, 'rgb(4, 5, 6)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(7, 8, 9)', 'replace') ] },
+                { property: 'border-top-color',
+                  values: [ valueFormat(0, 'rgb(4, 5, 6)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(7, 8, 9)', 'replace') ] },
+                { property: 'border-bottom-width',
+                  values: [ valueFormat(0, '2px', 'replace', 'linear'),
+                            valueFormat(1, '3px', 'replace') ] },
+                { property: 'border-left-width',
+                  values: [ valueFormat(0, '1px', 'replace', 'linear'),
+                            valueFormat(1, '3px', 'replace') ] },
+                { property: 'border-right-width',
+                  values: [ valueFormat(0, '2px', 'replace', 'linear'),
+                            valueFormat(1, '3px', 'replace') ] },
+                { property: 'border-top-width',
+                  values: [ valueFormat(0, '2px', 'replace', 'linear'),
+                            valueFormat(1, '3px', 'replace') ] },
+                { property: 'border-bottom-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-left-style',
+                  values: [ valueFormat(0, 'solid', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-right-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-top-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-image-outset',
+                  values: [ valueFormat(0, '0', 'replace', 'linear'),
+                            valueFormat(1, '0', 'replace') ] },
+                { property: 'border-image-repeat',
+                  values: [ valueFormat(0, 'stretch', 'replace', 'linear'),
+                            valueFormat(1, 'stretch', 'replace') ] },
+                { property: 'border-image-slice',
+                  values: [ valueFormat(0, '100%', 'replace', 'linear'),
+                            valueFormat(1, '100%', 'replace') ] },
+                { property: 'border-image-source',
+                  values: [ valueFormat(0, 'none', 'replace', 'linear'),
+                            valueFormat(1, 'none', 'replace') ] },
+                { property: 'border-image-width',
+                  values: [ valueFormat(0, '1', 'replace', 'linear'),
+                            valueFormat(1, '1', 'replace') ] },
+    ]
+  },
+  { desc:     'a keyframe sequence where greater shorthand precedes'
+              + ' lesser shorthand',
+    frames:   [ { offset: 0, border: '2px dotted rgb(4, 5, 6)',
+                             borderLeft: '1px solid rgb(1, 2, 3)' },
+                { offset: 1, border: '3px dashed rgb(7, 8, 9)' } ],
+    expected: [ { property: 'border-bottom-color',
+                  values: [ valueFormat(0, 'rgb(4, 5, 6)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(7, 8, 9)', 'replace') ] },
+                { property: 'border-left-color',
+                  values: [ valueFormat(0, 'rgb(1, 2, 3)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(7, 8, 9)', 'replace') ] },
+                { property: 'border-right-color',
+                  values: [ valueFormat(0, 'rgb(4, 5, 6)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(7, 8, 9)', 'replace') ] },
+                { property: 'border-top-color',
+                  values: [ valueFormat(0, 'rgb(4, 5, 6)', 'replace', 'linear'),
+                            valueFormat(1, 'rgb(7, 8, 9)', 'replace') ] },
+                { property: 'border-bottom-width',
+                  values: [ valueFormat(0, '2px', 'replace', 'linear'),
+                            valueFormat(1, '3px', 'replace') ] },
+                { property: 'border-left-width',
+                  values: [ valueFormat(0, '1px', 'replace', 'linear'),
+                            valueFormat(1, '3px', 'replace') ] },
+                { property: 'border-right-width',
+                  values: [ valueFormat(0, '2px', 'replace', 'linear'),
+                            valueFormat(1, '3px', 'replace') ] },
+                { property: 'border-top-width',
+                  values: [ valueFormat(0, '2px', 'replace', 'linear'),
+                            valueFormat(1, '3px', 'replace') ] },
+                { property: 'border-bottom-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-left-style',
+                  values: [ valueFormat(0, 'solid', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-right-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-top-style',
+                  values: [ valueFormat(0, 'dotted', 'replace', 'linear'),
+                            valueFormat(1, 'dashed', 'replace') ] },
+                { property: 'border-image-outset',
+                  values: [ valueFormat(0, '0', 'replace', 'linear'),
+                            valueFormat(1, '0', 'replace') ] },
+                { property: 'border-image-repeat',
+                  values: [ valueFormat(0, 'stretch', 'replace', 'linear'),
+                            valueFormat(1, 'stretch', 'replace') ] },
+                { property: 'border-image-slice',
+                  values: [ valueFormat(0, '100%', 'replace', 'linear'),
+                            valueFormat(1, '100%', 'replace') ] },
+                { property: 'border-image-source',
+                  values: [ valueFormat(0, 'none', 'replace', 'linear'),
+                            valueFormat(1, 'none', 'replace') ] },
+                { property: 'border-image-width',
+                  values: [ valueFormat(0, '1', 'replace', 'linear'),
+                            valueFormat(1, '1', 'replace') ] },
+    ]
+  },
+
+  // ---------------------------------------------------------------------
+  //
+  // Tests for unit conversion
+  //
+  // ---------------------------------------------------------------------
+
+  { desc:     'em units are resolved to px values',
+    frames:   { left: ['10em', '20em'] },
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '100px', 'replace', 'linear'),
+                            valueFormat(1, '200px', 'replace') ] } ]
+  },
+  { desc:     'calc() expressions are resolved to the equivalent units',
+    frames:   { left: ['calc(10em + 10px)', 'calc(10em + 10%)'] },
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '110px', 'replace', 'linear'),
+                            valueFormat(1, 'calc(10% + 100px)', 'replace') ] } ]
+  },
+
+  // ---------------------------------------------------------------------
+  //
+  // Tests for CSS variable handling conversion
+  //
+  // ---------------------------------------------------------------------
+
+  { desc:     'CSS variables are resolved to their corresponding values',
+    frames:   { left: ['10px', 'var(--var-100px)'] },
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '100px', 'replace') ] } ]
+  },
+  { desc:     'CSS variables in calc() expressions are resolved',
+    frames:   { left: ['10px', 'calc(var(--var-100px) / 2 - 10%)'] },
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, 'calc(-10% + 50px)', 'replace') ] } ]
+  },
+  { desc:     'CSS variables in shorthands are resolved to their corresponding'
+              + ' values',
+    frames:   { margin: ['10px', 'var(--var-100px-200px)'] },
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '100px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '200px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '100px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '200px', 'replace') ] } ]
+  },
+
+  // ---------------------------------------------------------------------
+  //
+  // Tests for properties that parse correctly but which we fail to
+  // convert to computed values.
+  //
+  // ---------------------------------------------------------------------
+
+  { desc:     'a missing property in initial keyframe',
+    frames:   [ { },
+                { margin: '5px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a missing property in initial keyframe and there are some ' +
+              'keyframes with the same offset',
+    frames:   [ { },
+                { margin: '10px', offset: 0.5 },
+                { margin: '20px', offset: 0.5 },
+                { margin: '30px'} ],
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(0.5, '10px',  'replace'),
+                            valueFormat(0.5, '20px',  'replace', 'linear'),
+                            valueFormat(1,   '30px',  'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(0.5, '10px',  'replace'),
+                            valueFormat(0.5, '20px',  'replace', 'linear'),
+                            valueFormat(1,   '30px',  'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(0.5, '10px',  'replace'),
+                            valueFormat(0.5, '20px',  'replace', 'linear'),
+                            valueFormat(1,   '30px',  'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(0.5, '10px',  'replace'),
+                            valueFormat(0.5, '20px',  'replace', 'linear'),
+                            valueFormat(1,   '30px',  'replace') ] } ]
+  },
+  { desc:     'a missing property in final keyframe',
+    frames:   [ { margin: '5px' },
+                { } ],
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] } ]
+  },
+  { desc:     'a missing property in final keyframe and there are some ' +
+              'keyframes with the same offsets',
+    frames:   [ { margin: '5px' },
+                { margin: '10px', offset: 0.5 },
+                { margin: '20px', offset: 0.5 },
+                { } ],
+    expected: [ { property: 'margin-top',
+                  values: [ valueFormat(0,   '5px', 'replace', 'linear'),
+                            valueFormat(0.5, '10px', 'replace'),
+                            valueFormat(0.5, '20px', 'replace', 'linear'),
+                            valueFormat(1,   undefined, 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(0.5, '10px', 'replace'),
+                            valueFormat(0.5, '20px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(0.5, '10px', 'replace'),
+                            valueFormat(0.5, '20px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(0.5, '10px', 'replace'),
+                            valueFormat(0.5, '20px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] } ]
+  },
+  { desc:     'a missing property in final keyframe where it forms the last'
+              + ' segment in the series',
+    frames:   [ { margin: '5px' },
+                { marginLeft: '5px',
+                  marginRight: '5px',
+                  marginBottom: '5px' } ],
+    expected: [ { property: 'margin-bottom',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-top',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] } ]
+  },
+  { desc:     'a missing property in initial keyframe along with other values',
+    frames:   [ {                left: '10px' },
+                { margin: '5px', left: '20px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '20px', 'replace') ] },
+                { property: 'margin-top',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a missing property in final keyframe along with other values',
+    frames:   [ { margin: '5px', left: '10px' },
+                {                left: '20px' } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '20px', 'replace') ] },
+                { property: 'margin-top',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] },
+                { property: 'margin-right',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] },
+                { property: 'margin-left',
+                  values: [ valueFormat(0, '5px', 'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] } ]
+  },
+  { desc:     'missing properties in both of initial and final keyframe',
+    frames:   [ { left: '5px', offset: 0.5 } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0,   undefined, 'replace', 'linear'),
+                            valueFormat(0.5, '5px',     'replace', 'linear'),
+                            valueFormat(1,   undefined, 'replace') ] } ]
+  },
+  { desc:     'missing propertes in both of initial and final keyframe along '
+              + 'with other values',
+    frames:   [ { left:  '5px',  offset: 0 },
+                { right: '5px',  offset: 0.5 },
+                { left:  '10px', offset: 1 } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '5px',  'replace', 'linear'),
+                            valueFormat(1, '10px', 'replace') ] },
+                { property: 'right',
+                  values: [ valueFormat(0,   undefined, 'replace', 'linear'),
+                            valueFormat(0.5, '5px',     'replace', 'linear'),
+                            valueFormat(1,   undefined, 'replace') ] } ]
+  },
+
+  { desc:     'a missing property in final keyframe with duplicate offset ' +
+              + 'along with other values',
+    frames:   [ { left: '5px',  right: '5px', offset: 0 },
+                { left: '8px',  right: '8px', offset: 0 },
+                { left: '10px',               offset: 1 } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '5px',  'replace'),
+                            valueFormat(0, '8px',  'replace', 'linear'),
+                            valueFormat(1, '10px', 'replace') ] },
+                { property: 'right',
+                  values: [ valueFormat(0, '5px',     'replace'),
+                            valueFormat(0, '8px',     'replace', 'linear'),
+                            valueFormat(1, undefined, 'replace') ] } ]
+  },
+
+  { desc:     'a missing property in initial keyframe with duplicate offset '
+              + 'along with other values',
+    frames:   [ { left: '10px',              offset: 0 },
+                { left: '8px', right: '8px', offset: 1 },
+                { left: '5px', right: '5px', offset: 1 } ],
+    expected: [ { property: 'left',
+                  values: [ valueFormat(0, '10px', 'replace', 'linear'),
+                            valueFormat(1, '8px',  'replace'),
+                            valueFormat(1, '5px',  'replace') ] },
+                { property: 'right',
+                  values: [ valueFormat(0, undefined, 'replace', 'linear'),
+                            valueFormat(1, '8px',     'replace'),
+                            valueFormat(1, '5px',     'replace') ] } ]
+  },
+];
+
+SpecialPowers.pushPrefEnv(
+  {
+    set: [
+      ["dom.animations-api.core.enabled", true],
+      ["dom.animations-api.implicit-keyframes.enabled", true],
+    ],
+  },
+  function() {
+    gTests.forEach(function(subtest) {
+      test(function(t) {
+        var div = addDiv(t);
+        var animation = div.animate(subtest.frames, 100 * MS_PER_SEC);
+        // Flush styles since getProperties currently does not. Rather, it
+        // returns the actual properties in use at the current time.
+        // However, we want to test what these properties will look like
+        // after the next restyle.
+        getComputedStyle(div).opacity;
+        assert_properties_equal(
+          animation.effect.getProperties(),
+          subtest.expected
+        );
+      }, subtest.desc);
+    });
+
+    done();
+  }
+);
+
+</script>
+</body>
diff --git a/dom/animation/test/chrome/test_animation_properties_display.html b/dom/animation/test/chrome/test_animation_properties_display.html
new file mode 100644
index 0000000000..184fc9d3bc
--- /dev/null
+++ b/dom/animation/test/chrome/test_animation_properties_display.html
@@ -0,0 +1,43 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Bug 1536688 - Test that 'display' is not included in
+  KeyframeEffect.getProperties() when using shorthand 'all'</title>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+</head>
+<body>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1536688"
+  target="_blank">Mozilla Bug 1536688</a>
+<div id="log"></div>
+<script>
+'use strict';
+
+SpecialPowers.pushPrefEnv(
+  {
+    set: [['dom.animations-api.core.enabled', true]],
+  },
+  function() {
+    test(t => {
+      const div = addDiv(t);
+      const animation = div.animate(
+        { all: ['unset', 'unset'] },
+        100 * MS_PER_SEC
+      );
+      // Flush styles since getProperties does not.
+      getComputedStyle(div).opacity;
+
+      const properties = animation.effect.getProperties();
+      assert_false(
+        properties.some(property => property.property === 'display'),
+        'Should not have a property for display'
+      );
+    });
+
+    done();
+  }
+);
+
+</script>
+</body>
diff --git a/dom/animation/test/chrome/test_cssanimation_missing_keyframes.html b/dom/animation/test/chrome/test_cssanimation_missing_keyframes.html
new file mode 100644
index 0000000000..1d19386712
--- /dev/null
+++ b/dom/animation/test/chrome/test_cssanimation_missing_keyframes.html
@@ -0,0 +1,73 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Bug 1339332 - Test for missing keyframes in CSS Animation</title>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+</head>
+<body>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1339332"
+   target="_blank">Mozilla Bug 1339332</a>
+<div id="log"></div>
+<style>
+@keyframes missingFrom {
+  to {
+    text-align: right;
+  }
+}
+@keyframes missingBoth {
+  50% {
+    text-align: right;
+  }
+}
+@keyframes missingTo {
+  from {
+    text-align: right;
+  }
+}
+</style>
+<script>
+'use strict';
+
+const gTests = [
+  { desc: 'missing "from" keyframe',
+    animationName: 'missingFrom',
+    expected: [{ property: 'text-align',
+                 values: [valueFormat(0, undefined, 'replace', 'ease'),
+                          valueFormat(1, 'right',   'replace')] } ]
+  },
+  { desc: 'missing "to" keyframe',
+    animationName: 'missingTo',
+    expected: [{ property: 'text-align',
+                 values: [valueFormat(0, 'right',   'replace', 'ease'),
+                          valueFormat(1, undefined, 'replace')] } ]
+  },
+  { desc: 'missing "from" and "to" keyframes',
+    animationName: 'missingBoth',
+    expected: [{ property: 'text-align',
+                 values: [valueFormat(0,  undefined, 'replace', 'ease'),
+                          valueFormat(.5, 'right',   'replace', 'ease'),
+                          valueFormat(1,  undefined, 'replace')] } ]
+  },
+];
+
+SpecialPowers.pushPrefEnv(
+  { set: [["dom.animations-api.core.enabled", true]] },
+  function() {
+    gTests.forEach(function(subtest) {
+      test(function(t) {
+        const div = addDiv(t);
+        div.style.animation = `${ subtest.animationName } 1000s`;
+        const animation = div.getAnimations()[0];
+        assert_properties_equal(animation.effect.getProperties(),
+                                subtest.expected);
+      }, subtest.desc);
+    });
+
+    done();
+  }
+);
+
+</script>
+</body>
diff --git a/dom/animation/test/chrome/test_generated_content_getAnimations.html b/dom/animation/test/chrome/test_generated_content_getAnimations.html
new file mode 100644
index 0000000000..08de27f57d
--- /dev/null
+++ b/dom/animation/test/chrome/test_generated_content_getAnimations.html
@@ -0,0 +1,83 @@
+<!DOCTYPE html>
+<head>
+<meta charset=utf-8>
+<title>Test getAnimations() for generated-content elements</title>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+<style>
+@keyframes anim { }
+@keyframes anim2 { }
+.before::before {
+  content: '';
+  animation: anim 100s;
+}
+.after::after {
+  content: '';
+  animation: anim 100s, anim2 100s;
+}
+</style>
+</head>
+<body>
+<div id='root' class='before after'>
+  <div class='before'></div>
+  <div></div>
+</div>
+<script>
+'use strict';
+
+const {Cc, Ci, Cu} = SpecialPowers;
+
+function getWalker(node) {
+  var walker = Cc["@mozilla.org/inspector/deep-tree-walker;1"].
+    createInstance(Ci.inIDeepTreeWalker);
+  walker.showAnonymousContent = true;
+  walker.init(node.ownerDocument, NodeFilter.SHOW_ALL);
+  walker.currentNode = node;
+  return walker;
+}
+
+test(function(t) {
+  var root = document.getElementById('root');
+  // Flush first to make sure the generated-content elements are ready
+  // in the tree.
+  flushComputedStyle(root);
+  var before = getWalker(root).firstChild();
+  var after = getWalker(root).lastChild();
+
+  // Sanity Checks
+  assert_equals(document.getAnimations().length, 4,
+                'All animations in this document');
+  assert_equals(before.tagName, '_moz_generated_content_before',
+                'First child is ::before element');
+  assert_equals(after.tagName, '_moz_generated_content_after',
+                'Last child is ::after element');
+
+  // Test Element.getAnimations() for generated-content elements
+  assert_equals(before.getAnimations().length, 1,
+                'Animations of ::before generated-content element');
+  assert_equals(after.getAnimations().length, 2,
+                'Animations of ::after generated-content element');
+}, 'Element.getAnimations() used on generated-content elements');
+
+test(function(t) {
+  var root = document.getElementById('root');
+  flushComputedStyle(root);
+  var walker = getWalker(root);
+
+  var animations = [];
+  var element = walker.currentNode;
+  while (element) {
+    if (element.getAnimations) {
+      animations = [...animations, ...element.getAnimations()];
+    }
+    element = walker.nextNode();
+  }
+
+  assert_equals(animations.length, document.getAnimations().length,
+                'The number of animations got by DeepTreeWalker and ' +
+                'document.getAnimations() should be the same');
+}, 'Element.getAnimations() used by traversing DeepTreeWalker');
+
+</script>
+</body>
diff --git a/dom/animation/test/chrome/test_keyframe_effect_xrays.html b/dom/animation/test/chrome/test_keyframe_effect_xrays.html
new file mode 100644
index 0000000000..ca3e712ac5
--- /dev/null
+++ b/dom/animation/test/chrome/test_keyframe_effect_xrays.html
@@ -0,0 +1,45 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+</head>
+<body>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1414674"
+  target="_blank">Mozilla Bug 1414674</a>
+<div id="log"></div>
+<iframe id="iframe"
+  src="http://example.org/tests/dom/animation/test/chrome/file_animate_xrays.html"></iframe>
+<script>
+'use strict';
+
+var win = document.getElementById('iframe').contentWindow;
+
+async_test(function(t) {
+  window.addEventListener('load', t.step_func(function() {
+    var target = win.document.getElementById('target');
+    var effect = new win.KeyframeEffect(target, [
+      {opacity: 1, offset: 0},
+      {opacity: 0, offset: 1},
+    ], {duration: 100 * MS_PER_SEC, fill: "forwards"});
+    // The frames object should be accessible via x-ray.
+    var frames = effect.getKeyframes();
+    assert_equals(frames.length, 2,
+                  "frames for KeyframeEffect ctor should be non-zero");
+    assert_equals(frames[0].opacity, "1",
+                  "first frame opacity for KeyframeEffect ctor should be specified value");
+    assert_equals(frames[0].computedOffset, 0,
+                  "first frame offset for KeyframeEffect ctor should be 0");
+    assert_equals(frames[1].opacity, "0",
+                  "last frame opacity for KeyframeEffect ctor should be specified value");
+    assert_equals(frames[1].computedOffset, 1,
+                  "last frame offset for KeyframeEffect ctor should be 1");
+    var animation = new win.Animation(effect, document.timeline);
+    animation.play();
+    t.done();
+  }));
+}, 'Calling KeyframeEffect() ctor across x-rays');
+
+</script>
+</body>
diff --git a/dom/animation/test/chrome/test_mutation_observer_for_element_removal_in_shadow_tree.html b/dom/animation/test/chrome/test_mutation_observer_for_element_removal_in_shadow_tree.html
new file mode 100644
index 0000000000..f8efaa6baf
--- /dev/null
+++ b/dom/animation/test/chrome/test_mutation_observer_for_element_removal_in_shadow_tree.html
@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+<div id="log"></div>
+<script>
+
+promise_test(async t => {
+  // Set up a MutationObserver for animations.
+  const observer = new MutationObserver(() => {});
+  observer.observe(document.documentElement, {
+    animations: true,
+    subtree: true,
+  });
+
+  // Create a CSS transition in a shadow tree.
+  let s = document.createElement('shadow-test');
+  document.documentElement.appendChild(s);
+  s.attachShadow({mode:"open"});
+
+  let property = 'opacity';
+  let initial = '1';
+  let finalValue = '0';
+
+  let div = document.createElement('div');
+  div.style = `${property}:${initial};transition:${property} 2s;`
+
+  s.shadowRoot.appendChild(div);
+  div.offsetWidth;
+
+  div.style[property] = finalValue;
+
+  const eventWatcher = new EventWatcher(t, div, ['transitionstart']);
+
+  // Trigger a CSS transition.
+  getComputedStyle(div)[property];
+
+  // Wait for a transitionend event to make sure the transition has been started.
+  await eventWatcher.wait_for('transitionstart');
+
+  // Now remove the element to notify it to the observer
+  div.parentNode.removeChild(div);
+});
+</script>
diff --git a/dom/animation/test/chrome/test_running_on_compositor.html b/dom/animation/test/chrome/test_running_on_compositor.html
new file mode 100644
index 0000000000..532c11258f
--- /dev/null
+++ b/dom/animation/test/chrome/test_running_on_compositor.html
@@ -0,0 +1,1516 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Bug 1045994 - Add a chrome-only property to inspect if an animation is
+       running on the compositor or not</title>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+<style>
+@keyframes anim {
+  to { transform: translate(100px) }
+}
+@keyframes transform-starts-with-none {
+    0% { transform: none }
+   99% { transform: none }
+  100% { transform: translate(100px) }
+}
+@keyframes opacity {
+  to { opacity: 0 }
+}
+@keyframes zIndex_and_translate {
+  to { z-index: 999; transform: translate(100px); }
+}
+@keyframes z-index {
+  to { z-index: 999; }
+}
+@keyframes rotate {
+  from { transform: rotate(0deg); }
+  to { transform: rotate(360deg); }
+}
+@keyframes rotate-and-opacity {
+  from { transform: rotate(0deg); opacity: 1;}
+  to { transform: rotate(360deg); opacity: 0;}
+}
+div {
+  /* Element needs geometry to be eligible for layerization */
+  width: 100px;
+  height: 100px;
+  background-color: white;
+}
+</style>
+</head>
+<body>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1045994"
+  target="_blank">Mozilla Bug 1045994</a>
+<div id="log"></div>
+<script>
+'use strict';
+
+/** Test for bug 1045994 - Add a chrome-only property to inspect if an
+    animation is running on the compositor or not **/
+
+const omtaEnabled = isOMTAEnabled();
+
+function assert_animation_is_running_on_compositor(animation, desc) {
+  assert_equals(animation.isRunningOnCompositor, omtaEnabled,
+                desc + ' at ' + animation.currentTime + 'ms');
+}
+
+function assert_animation_is_not_running_on_compositor(animation, desc) {
+  assert_equals(animation.isRunningOnCompositor, false,
+                desc + ' at ' + animation.currentTime + 'ms');
+}
+
+promise_test(async t => {
+  // FIXME: When we implement Element.animate, use that here instead of CSS
+  // so that we remove any dependency on the CSS mapping.
+  var div = addDiv(t, { style: 'animation: anim 100s' });
+  var animation = div.getAnimations()[0];
+
+  // If the animation starts at the current timeline time, we need to wait for
+  // one more frame to avoid receiving the fake timer-based MozAfterPaint event.
+  // FIXME: Bug 1419226: Drop this 'animation.ready' and 'waitForFrame'.  Once
+  // MozAfterPaint is fired reliably, we just need to wait for a MozAfterPaint
+  // here.
+  await animation.ready;
+
+  if (animationStartsRightNow(animation)) {
+    await waitForNextFrame();
+  }
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+     'Animation reports that it is running on the compositor'
+     + ' during playback');
+
+  div.style.animationPlayState = 'paused';
+
+  await animation.ready;
+
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' when paused');
+}, '');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: z-index 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' for animation of "z-index"');
+}, 'isRunningOnCompositor is false for animation of "z-index"');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: zIndex_and_translate 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+     'Animation reports that it is running on the compositor'
+      + ' when the animation has two properties, where one can run'
+      + ' on the compositor, the other cannot');
+}, 'isRunningOnCompositor is true if the animation has at least one ' +
+   'property can run on compositor');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: anim 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  animation.pause();
+  await animation.ready;
+
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' when animation.pause() is called');
+}, 'isRunningOnCompositor is false when the animation.pause() is called');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: anim 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  animation.finish();
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' immediately after animation.finish() is called');
+  // Check that we don't set the flag back again on the next tick.
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' on the next tick after animation.finish() is called');
+}, 'isRunningOnCompositor is false when the animation.finish() is called');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: anim 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  animation.currentTime = 100 * MS_PER_SEC;
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' immediately after manually seeking the animation to the end');
+  // Check that we don't set the flag back again on the next tick.
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' on the next tick after manually seeking the animation to the end');
+}, 'isRunningOnCompositor is false when manually seeking the animation to ' +
+   'the end');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: anim 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  animation.cancel();
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' immediately after animation.cancel() is called');
+  // Check that we don't set the flag back again on the next tick.
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' on the next tick after animation.cancel() is called');
+}, 'isRunningOnCompositor is false when animation.cancel() is called');
+
+// This is to test that we don't simply clobber the flag when ticking
+// animations and then set it again during painting.
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: anim 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  await new Promise(resolve => {
+    window.requestAnimationFrame(() => {
+      t.step(() => {
+        assert_animation_is_running_on_compositor(animation,
+          'Animation reports that it is running on the compositor'
+           + ' in requestAnimationFrame callback');
+      });
+
+      resolve();
+    });
+  });
+}, 'isRunningOnCompositor is true in requestAnimationFrame callback');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: anim 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  await new Promise(resolve => {
+    var observer = new MutationObserver(records => {
+      var changedAnimation;
+
+      records.forEach(record => {
+        changedAnimation =
+          record.changedAnimations.find(changedAnim => {
+            return changedAnim == animation;
+          });
+      });
+
+      t.step(() => {
+        assert_true(!!changedAnimation, 'The animation should be recorded '
+          + 'as one of the changedAnimations');
+
+        assert_animation_is_running_on_compositor(animation,
+          'Animation reports that it is running on the compositor'
+           + ' in MutationObserver callback');
+      });
+
+      resolve();
+    });
+    observer.observe(div, { animations: true, subtree: false });
+    t.add_cleanup(() => {
+      observer.disconnect();
+    });
+    div.style.animationDuration = "200s";
+  });
+}, 'isRunningOnCompositor is true in MutationObserver callback');
+
+// This is to test that we don't temporarily clear the flag when forcing
+// an unthrottled sample.
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: rotate 100s' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  await new Promise(resolve => {
+    var timeAtStart = window.performance.now();
+    function handleFrame() {
+      t.step(() => {
+        assert_animation_is_running_on_compositor(animation,
+          'Animation reports that it is running on the compositor'
+           + ' in requestAnimationFrame callback');
+      });
+
+      // we have to wait at least 200ms because this animation is
+      // unthrottled on every 200ms.
+      // See https://hg.mozilla.org/mozilla-central/file/cafb1c90f794/layout/style/AnimationCommon.cpp#l863
+      if (window.performance.now() - timeAtStart > 200) {
+        resolve();
+        return;
+      }
+      window.requestAnimationFrame(handleFrame);
+    }
+    window.requestAnimationFrame(handleFrame);
+  });
+}, 'isRunningOnCompositor remains true in requestAnimationFrameCallback for ' +
+   'overflow animation');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'transition: opacity 100s; opacity: 1' });
+
+  getComputedStyle(div).opacity;
+
+  div.style.opacity = 0;
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+     'Transition reports that it is running on the compositor'
+     + ' during playback for opacity transition');
+}, 'isRunningOnCompositor for transitions');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'animation: rotate-and-opacity 100s; ' +
+                               'backface-visibility: hidden; ' +
+                               'transform: none !important;' });
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+     'If an animation has a property that can run on the compositor and a '
+     + 'property that cannot (due to Gecko limitations) but where the latter'
+     + 'property is overridden in the CSS cascade, the animation should '
+     + 'still report that it is running on the compositor');
+}, 'isRunningOnCompositor is true when a property that would otherwise block ' +
+   'running on the compositor is overridden in the CSS cascade');
+
+promise_test(async t => {
+  var animation = addDivAndAnimate(t,
+                                   {},
+                                   { opacity: [ 0, 1 ] }, 200 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation reports that it is running on the compositor');
+
+  animation.currentTime = 150 * MS_PER_SEC;
+  animation.effect.updateTiming({ duration: 100 * MS_PER_SEC });
+
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation reports that it is NOT running on the compositor'
+     + ' when the animation is set a shorter duration than current time');
+}, 'animation is immediately removed from compositor' +
+   'when the duration is made shorter than the current time');
+
+promise_test(async t => {
+  var animation = addDivAndAnimate(t,
+                                   {},
+                                   { opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation reports that it is running on the compositor');
+
+  animation.currentTime = 500 * MS_PER_SEC;
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Animation reports that it is NOT running on the compositor'
+    + ' when finished');
+
+  animation.effect.updateTiming({ duration: 1000 * MS_PER_SEC });
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation reports that it is running on the compositor'
+    + ' when restarted');
+}, 'animation is added to compositor' +
+   ' when the duration is made longer than the current time');
+
+promise_test(async t => {
+  var animation = addDivAndAnimate(t,
+                                   {},
+                                   { opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation reports that it is running on the compositor');
+
+  animation.effect.updateTiming({ endDelay: 100 * MS_PER_SEC });
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation reports that it is running on the compositor'
+    + ' when endDelay is changed');
+
+  animation.currentTime = 110 * MS_PER_SEC;
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Animation reports that it is NOT running on the compositor'
+    + ' when currentTime is during endDelay');
+}, 'animation is removed from compositor' +
+   ' when current time is made longer than the duration even during endDelay');
+
+promise_test(async t => {
+  var animation = addDivAndAnimate(t,
+                                   {},
+                                   { opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation reports that it is running on the compositor');
+
+  animation.effect.updateTiming({ endDelay: -200 * MS_PER_SEC });
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Animation reports that it is NOT running on the compositor'
+    + ' when endTime is negative value');
+}, 'animation is removed from compositor' +
+   ' when endTime is negative value');
+
+promise_test(async t => {
+  var animation = addDivAndAnimate(t,
+                                   {},
+                                   { opacity: [ 0, 1 ] }, 200 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation reports that it is running on the compositor');
+
+  animation.effect.updateTiming({ endDelay: -100 * MS_PER_SEC });
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation reports that it is running on the compositor'
+    + ' when endTime is positive and endDelay is negative');
+  animation.currentTime = 110 * MS_PER_SEC;
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Animation reports that it is NOT running on the compositor'
+    + ' when currentTime is after endTime');
+}, 'animation is NOT running on compositor' +
+   ' when endTime is positive and endDelay is negative');
+
+promise_test(async t => {
+  var effect = new KeyframeEffect(null,
+                                  { opacity: [ 0, 1 ] },
+                                  100 * MS_PER_SEC);
+  var animation = new Animation(effect, document.timeline);
+  animation.play();
+
+  var div = addDiv(t);
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+                'Animation with null target reports that it is not running ' +
+                'on the compositor');
+
+  animation.effect.target = div;
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+                'Animation reports that it is running on the compositor ' +
+                'after setting a valid target');
+}, 'animation is added to the compositor when setting a valid target');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var animation = div.animate({ opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+                'Animation reports that it is running on the compositor');
+
+  animation.effect.target = null;
+  assert_animation_is_not_running_on_compositor(animation,
+                'Animation reports that it is NOT running on the ' +
+                'compositor after setting null target');
+}, 'animation is removed from the compositor when setting null target');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var animation = div.animate({ opacity: [ 0, 1 ] },
+                              { duration: 100 * MS_PER_SEC,
+                                delay: 100 * MS_PER_SEC,
+                                fill: 'backwards' });
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+                'Animation with fill:backwards in delay phase reports ' +
+                'that it is running on the compositor');
+
+  animation.currentTime = 100 * MS_PER_SEC;
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+      'Animation with fill:backwards in delay phase reports ' +
+      'that it is running on the compositor after delay phase');
+}, 'animation with fill:backwards in delay phase is running on the ' +
+   ' compositor while it is in delay phase');
+
+promise_test(async t => {
+  const animation = addDiv(t).animate({ opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+  animation.playbackRate = -1;
+  animation.currentTime = 200 * MS_PER_SEC;
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+                'Animation with negative playback rate is runnning on the'
+                + ' compositor even before it reaches the active interval');
+}, 'animation with negative playback rate is sent to the compositor even in'
+   + ' after phase');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var animation = div.animate([{ opacity: 1, offset: 0 },
+                               { opacity: 1, offset: 0.99 },
+                               { opacity: 0, offset: 1 }], 100 * MS_PER_SEC);
+
+  var another = addDiv(t);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+                'Opacity animation on a 100% opacity keyframe reports ' +
+                'that it is running on the compositor from the begining');
+
+  animation.effect.target = another;
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+                'Opacity animation on a 100% opacity keyframe keeps ' +
+                'running on the compositor after changing the target ' +
+                'element');
+}, '100% opacity animations with keeps running on the ' +
+   'compositor after changing the target element');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var animation = div.animate({ color: ['red', 'black'] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+                'Color animation reports that it is not running on the ' +
+                'compositor');
+
+  animation.effect.setKeyframes([{ opacity: 1, offset: 0 },
+                                 { opacity: 1, offset: 0.99 },
+                                 { opacity: 0, offset: 1 }]);
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+                '100% opacity animation set by using setKeyframes reports ' +
+                'that it is running on the compositor');
+}, '100% opacity animation set up by converting an existing animation with ' +
+   'cannot be run on the compositor, is running on the compositor');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var animation = div.animate({ color: ['red', 'black'] }, 100 * MS_PER_SEC);
+  var effect = new KeyframeEffect(div,
+                                  [{ opacity: 1, offset: 0 },
+                                   { opacity: 1, offset: 0.99 },
+                                   { opacity: 0, offset: 1 }],
+                                  100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+                'Color animation reports that it is not running on the ' +
+                'compositor');
+
+  animation.effect = effect;
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+                '100% opacity animation set up by changing effects reports ' +
+                'that it is running on the compositor');
+}, '100% opacity animation set up by changing the effects on an existing ' +
+   'animation which cannot be run on the compositor, is running on the ' +
+   'compositor');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: "opacity: 1 ! important" });
+
+  var animation = div.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Opacity animation on an element which has 100% opacity style with ' +
+    '!important flag reports that it is not running on the compositor');
+  // Clear important flag from the opacity style on the target element.
+  div.style.setProperty("opacity", "1", "");
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Opacity animation reports that it is running on the compositor after '
+    + 'clearing the !important flag');
+}, 'Clearing *important* opacity style on the target element sends the ' +
+   'animation to the compositor');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var lowerAnimation = div.animate({ opacity: [1, 0] }, 100 * MS_PER_SEC);
+  var higherAnimation = div.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(higherAnimation,
+                'A higher-priority opacity animation on an element ' +
+                'reports that it is running on the compositor');
+  assert_animation_is_running_on_compositor(lowerAnimation,
+                'A lower-priority opacity animation on the same ' +
+                'element also reports that it is running on the compositor');
+}, 'Opacity animations on the same element run on the compositor');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'transition: opacity 100s; opacity: 1' });
+
+  getComputedStyle(div).opacity;
+
+  div.style.opacity = 0;
+  getComputedStyle(div).opacity;
+
+  var transition = div.getAnimations()[0];
+  var animation = div.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+                'An opacity animation on an element reports that' +
+                'that it is running on the compositor');
+  assert_animation_is_running_on_compositor(transition,
+                'An opacity transition on the same element reports that ' +
+                'it is running on the compositor');
+}, 'Both of transition and script animation on the same element run on the ' +
+   'compositor');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var importantOpacityElement = addDiv(t, { style: "opacity: 1 ! important" });
+
+  var animation = div.animate({ opacity: [1, 0] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+                'Opacity animation on an element reports ' +
+                'that it is running on the compositor');
+
+  animation.effect.target = null;
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(animation,
+                'Animation is no longer running on the compositor after ' +
+                'removing from the element');
+  animation.effect.target = importantOpacityElement;
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(animation,
+                'Animation is NOT running on the compositor even after ' +
+                'being applied to a different element which has an ' +
+                '!important opacity declaration');
+}, 'Animation continues not running on the compositor after being ' +
+   'applied to an element which has an important declaration and ' +
+   'having previously been temporarily associated with no target element');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var another = addDiv(t);
+
+  var lowerAnimation = div.animate({ opacity: [1, 0] }, 100 * MS_PER_SEC);
+  var higherAnimation = another.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(lowerAnimation,
+                'An opacity animation on an element reports that ' +
+                'it is running on the compositor');
+  assert_animation_is_running_on_compositor(higherAnimation,
+                'Opacity animation on a different element reports ' +
+                'that it is running on the compositor');
+
+  lowerAnimation.effect.target = null;
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(lowerAnimation,
+                'Animation is no longer running on the compositor after ' +
+                'being removed from the element');
+  lowerAnimation.effect.target = another;
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(lowerAnimation,
+                'A lower-priority animation begins running ' +
+                'on the compositor after being applied to an element ' +
+                'which has a higher-priority animation');
+  assert_animation_is_running_on_compositor(higherAnimation,
+                'A higher-priority animation continues to run on the ' +
+                'compositor even after a lower-priority animation is ' +
+                'applied to the same element');
+}, 'Animation begins running on the compositor after being applied ' +
+   'to an element which has a higher-priority animation and after ' +
+   'being temporarily associated with no target element');
+
+promise_test(async t => {
+  var div = addDiv(t);
+  var another = addDiv(t);
+
+  var lowerAnimation = div.animate({ opacity: [1, 0] }, 100 * MS_PER_SEC);
+  var higherAnimation = another.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(lowerAnimation,
+                'An opacity animation on an element reports that ' +
+                'it is running on the compositor');
+  assert_animation_is_running_on_compositor(higherAnimation,
+                'Opacity animation on a different element reports ' +
+                'that it is running on the compositor');
+
+  higherAnimation.effect.target = null;
+  await waitForFrame();
+
+  assert_animation_is_not_running_on_compositor(higherAnimation,
+                'Animation is no longer running on the compositor after ' +
+                'being removed from the element');
+  higherAnimation.effect.target = div;
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(lowerAnimation,
+                'Animation continues running on the compositor after ' +
+                'a higher-priority animation applied to the same element');
+  assert_animation_is_running_on_compositor(higherAnimation,
+                'A higher-priority animation begins to running on the ' +
+                'compositor after being applied to an element which has ' +
+                'a lower-priority-animation');
+}, 'Animation begins running on the compositor after being applied ' +
+   'to an element which has a lower-priority animation once after ' +
+   'disassociating with an element');
+
+var delayPhaseTests = [
+  {
+    desc: 'script animation of opacity',
+    setupAnimation: t => {
+      return addDiv(t).animate(
+        { opacity: [0, 1] },
+        { delay: 100 * MS_PER_SEC, duration: 100 * MS_PER_SEC });
+    },
+  },
+  {
+    desc: 'script animation of transform',
+    setupAnimation: t => {
+      return addDiv(t).animate(
+        { transform: ['translateX(0px)', 'translateX(100px)'] },
+        { delay: 100 * MS_PER_SEC, duration: 100 * MS_PER_SEC });
+    },
+  },
+  {
+    desc: 'CSS animation of opacity',
+    setupAnimation: t => {
+      return addDiv(t, { style: 'animation: opacity 100s 100s' })
+        .getAnimations()[0];
+    },
+  },
+  {
+    desc: 'CSS animation of transform',
+    setupAnimation: t => {
+      return addDiv(t, { style: 'animation: anim 100s 100s' })
+        .getAnimations()[0];
+    },
+  },
+  {
+    desc: 'CSS transition of opacity',
+    setupAnimation: t => {
+      var div = addDiv(t, { style: 'transition: opacity 100s 100s' });
+      getComputedStyle(div).opacity;
+
+      div.style.opacity = 0;
+      return div.getAnimations()[0];
+    },
+  },
+  {
+    desc: 'CSS transition of transform',
+    setupAnimation: t => {
+      var div = addDiv(t, { style: 'transition: transform 100s 100s' });
+      getComputedStyle(div).transform;
+
+      div.style.transform = 'translateX(100px)';
+      return div.getAnimations()[0];
+    },
+  },
+];
+
+delayPhaseTests.forEach(test => {
+  promise_test(async t => {
+    var animation = test.setupAnimation(t);
+
+    await waitForPaints();
+
+    assert_animation_is_running_on_compositor(animation,
+       test.desc + ' reports that it is running on the '
+       + 'compositor even though it is in the delay phase');
+  }, 'isRunningOnCompositor for ' + test.desc + ' is true even though ' +
+     'it is in the delay phase');
+});
+
+// The purpose of thie test cases is to check that
+// NS_FRAME_MAY_BE_TRANSFORMED flag on the associated nsIFrame persists
+// after transform style on the frame is removed.
+var delayPhaseWithTransformStyleTests = [
+  {
+    desc: 'script animation of transform with transform style',
+    setupAnimation: t => {
+      return addDiv(t, { style: 'transform: translateX(10px)' }).animate(
+        { transform: ['translateX(0px)', 'translateX(100px)'] },
+        { delay: 100 * MS_PER_SEC, duration: 100 * MS_PER_SEC });
+    },
+  },
+  {
+    desc: 'CSS animation of transform with transform style',
+    setupAnimation: t => {
+      return addDiv(t, { style: 'animation: anim 100s 100s;' +
+                                'transform: translateX(10px)' })
+        .getAnimations()[0];
+    },
+  },
+  {
+    desc: 'CSS transition of transform with transform style',
+    setupAnimation: t => {
+      var div = addDiv(t, { style: 'transition: transform 100s 100s;' +
+                                   'transform: translateX(10px)'});
+      getComputedStyle(div).transform;
+
+      div.style.transform = 'translateX(100px)';
+      return div.getAnimations()[0];
+    },
+  },
+];
+
+delayPhaseWithTransformStyleTests.forEach(test => {
+  promise_test(async t => {
+    var animation = test.setupAnimation(t);
+
+    await waitForPaints();
+
+    assert_animation_is_running_on_compositor(animation,
+       test.desc + ' reports that it is running on the '
+       + 'compositor even though it is in the delay phase');
+
+    // Remove the initial transform style during delay phase.
+    animation.effect.target.style.transform = 'none';
+    await animation.ready;
+
+    assert_animation_is_running_on_compositor(animation,
+       test.desc + ' reports that it keeps running on the '
+       + 'compositor after removing the initial transform style');
+  }, 'isRunningOnCompositor for ' + test.desc + ' is true after removing ' +
+     'the initial transform style during the delay phase');
+});
+
+var startsWithNoneTests = [
+  {
+    desc: 'script animation of transform starts with transform:none segment',
+    setupAnimation: t => {
+      return addDiv(t).animate(
+        { transform: ['none', 'none', 'translateX(100px)'] }, 100 * MS_PER_SEC);
+    },
+  },
+  {
+    desc: 'CSS animation of transform starts with transform:none segment',
+    setupAnimation: t => {
+      return addDiv(t,
+        { style: 'animation: transform-starts-with-none 100s 100s' })
+          .getAnimations()[0];
+    },
+  },
+];
+
+startsWithNoneTests.forEach(test => {
+  promise_test(async t => {
+    var animation = test.setupAnimation(t);
+
+    await waitForPaints();
+
+    assert_animation_is_running_on_compositor(animation,
+       test.desc + ' reports that it is running on the '
+       + 'compositor even though it is in transform:none segment');
+  }, 'isRunningOnCompositor for ' + test.desc + ' is true even though ' +
+     'it is in transform:none segment');
+});
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'opacity: 1 ! important' });
+
+  var animation = div.animate(
+    { opacity: [0, 1] },
+    { delay: 100 * MS_PER_SEC, duration: 100 * MS_PER_SEC });
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Opacity animation on an element which has opacity:1 important style'
+    + 'reports that it is not running on the compositor');
+  // Clear the opacity style on the target element.
+  div.style.setProperty("opacity", "1", "");
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Opacity animations reports that it is running on the compositor after '
+    + 'clearing the opacity style on the element');
+}, 'Clearing *important* opacity style on the target element sends the ' +
+   'animation to the compositor even if the animation is in the delay phase');
+
+promise_test(async t => {
+  var opaqueDiv = addDiv(t, { style: 'opacity: 1 ! important' });
+  var anotherDiv = addDiv(t);
+
+  var animation = opaqueDiv.animate(
+    { opacity: [0, 1] },
+    { delay: 100 * MS_PER_SEC, duration: 100 * MS_PER_SEC });
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Opacity animation on an element which has opacity:1 important style'
+    + 'reports that it is not running on the compositor');
+  // Changing target element to another element which has no opacity style.
+  animation.effect.target = anotherDiv;
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Opacity animations reports that it is running on the compositor after '
+    + 'changing the target element to another elemenent having no '
+    + 'opacity style');
+}, 'Changing target element of opacity animation sends the animation to the ' +
+   'the compositor even if the animation is in the delay phase');
+
+promise_test(async t => {
+  var animation =
+    addDivAndAnimate(t,
+                     {},
+                     { width: ['100px', '200px'] },
+                     { duration: 100 * MS_PER_SEC, delay: 100 * MS_PER_SEC });
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Width animation reports that it is not running on the compositor '
+    + 'in the delay phase');
+  // Changing to property runnable on the compositor.
+  animation.effect.setKeyframes({ opacity: [0, 1] });
+  await waitForFrame();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Opacity animation reports that it is running on the compositor '
+    + 'after changing the property from width property in the delay phase');
+}, 'Dynamic change to a property runnable on the compositor ' +
+   'in the delay phase');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'transition: opacity 100s; ' +
+                               'opacity: 0 !important' });
+  getComputedStyle(div).opacity;
+
+  div.style.setProperty('opacity', '1', 'important');
+  getComputedStyle(div).opacity;
+
+  var animation = div.getAnimations()[0];
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+     'Transition reports that it is running on the compositor even if the ' +
+     'property is overridden by an !important rule');
+}, 'Transitions override important rules');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'transition: opacity 100s; ' +
+                               'opacity: 0 !important' });
+  getComputedStyle(div).opacity;
+
+  div.animate({ opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+  div.style.setProperty('opacity', '1', 'important');
+  getComputedStyle(div).opacity;
+
+  var [transition, animation] = div.getAnimations();
+
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(transition,
+     'Transition suppressed by an animation which is overridden by an ' +
+     '!important rule reports that it is NOT running on the compositor');
+  assert_animation_is_not_running_on_compositor(animation,
+     'Animation overridden by an !important rule reports that it is ' +
+     'NOT running on the compositor');
+}, 'Neither transition nor animation does run on the compositor if the ' +
+   'property is overridden by an !important rule');
+
+promise_test(async t => {
+  var div = addDiv(t, { style: 'display: table' });
+  var animation =
+    div.animate({ transform: ['rotate(0deg)', 'rotate(360deg)'] },
+                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Transform animation on display:table element should be running on the'
+    + ' compositor');
+}, 'Transform animation on display:table element runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t, { style: 'display: table' });
+  const animation = div.animate(null, 100 * MS_PER_SEC);
+  const effect = new KeyframeEffect(div,
+                                    { transform: ['none', 'none']},
+                                    100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+
+  animation.effect = effect;
+
+  await waitForNextFrame();
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(
+    animation,
+    'Transform animation on table element should be running on the compositor'
+  );
+}, 'Empty transform effect assigned after the fact to display:table content'
+   + ' runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ backgroundColor: ['blue', 'green'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'background-color animation should be running on the compositor');
+}, 'background-color animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ backgroundColor: ['blue', 'green'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'background-color animation should be running on the compositor');
+
+  // Add a red opaque background image covering the background color animation.
+  div.style.backgroundImage =
+    'url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAIAAAAC64' +
+    'paAAAAG0lEQVR42mP8z0A%2BYKJA76jmUc2jmkc1U0EzACKcASfOgGoMAAAAAElFTkSuQmCC)';
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  // Bug 1712246. We should optimize this case eventually.
+  //assert_animation_is_not_running_on_compositor(animation,
+  //  'Opaque background image stops background-color animations from running ' +
+  //  'on the compositor');
+}, 'Opaque background image stops background-color animations from running ' +
+   ' on the compositor');
+
+promise_test(async t => {
+  await SpecialPowers.pushPrefEnv({
+    set: [["gfx.omta.background-color", false]]
+  });
+
+  const div = addDiv(t);
+  const animation = div.animate({ backgroundColor: ['blue', 'green'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'background-color animation should NOT be running on the compositor ' +
+    'if the pref is disabled');
+}, 'background-color animation does not run on the compositor if the pref ' +
+   'is disabled');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ translate: ['0px', '100px'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'translate animation should be running on the compositor');
+}, 'translate animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ rotate: ['0deg', '45deg'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'rotate animation should be running on the compositor');
+}, 'rotate animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ scale: ['1 1', '2 2'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'scale animation should be running on the compositor');
+}, 'scale animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ translate: ['0px', '100px'],
+                                  rotate: ['0deg', '45deg'],
+                                  transform: ['translate(20px)',
+                                              'translate(30px)'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'multiple transform-like properties animation should be running on the ' +
+    'compositor');
+
+  const properties = animation.effect.getProperties();
+  properties.forEach(property => {
+    assert_true(property.runningOnCompositor,
+                property.property + ' is running on the compositor');
+  });
+}, 'Multiple transform-like properties animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ offsetPath: ['none', 'none'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'offset-path animation should be running on the compositor even if ' +
+    'it is always none');
+}, 'offset-path none animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ offsetPath: ['path("M0 0l100 100")',
+                                               'path("M0 0l200 200")'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'offset-path animation should be running on the compositor');
+}, 'offset-path animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ offsetDistance: ['0%', '100%'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'offset-distance animation is not running on the compositor because ' +
+    'offset-path is none');
+
+  const newAnim = div.animate({ offsetPath: ['None', 'None'] },
+                              100 * MS_PER_SEC);
+  await waitForAnimationReadyToRestyle(newAnim);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'offset-distance animation should be running on the compositor');
+  assert_animation_is_running_on_compositor(newAnim,
+    'new added offset-path animation should be running on the compositor');
+}, 'offset-distance animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ offsetRotate: ['0deg', '45deg'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'offset-rotate animation is not running on the compositor because ' +
+    'offset-path is none');
+
+  const newAnim = div.animate({ offsetPath: ['None', 'None'] },
+                              100 * MS_PER_SEC);
+  await waitForAnimationReadyToRestyle(newAnim);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'offset-rotate animation should be running on the compositor');
+  assert_animation_is_running_on_compositor(newAnim,
+    'new added offset-path animation should be running on the compositor');
+}, 'offset-rotate animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ offsetAnchor: ['0% 0%', '100% 100%'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'offset-anchor animation is not running on the compositor because ' +
+    'offset-path is none');
+
+  const newAnim = div.animate({ offsetPath: ['None', 'None'] },
+                              100 * MS_PER_SEC);
+  await waitForAnimationReadyToRestyle(newAnim);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'offset-anchor animation should be running on the compositor');
+  assert_animation_is_running_on_compositor(newAnim,
+    'new added offset-path animation should be running on the compositor');
+}, 'offset-anchor animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ translate: ['0px', '100px'],
+                                  rotate: ['0deg', '45deg'],
+                                  transform: ['translate(0px)',
+                                              'translate(100px)'],
+                                  offsetDistance: ['0%', '100%'] },
+                                100 * MS_PER_SEC);
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation is running on the compositor even though we do not have ' +
+    'offset-path');
+
+  div.style.offsetPath = 'path("M50 0v100")';
+  getComputedStyle(div).offsetPath;
+
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation is running on the compositor');
+
+}, 'Multiple transform-like properties (include motion-path) animation runs ' +
+   'on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ translate: ['0px', '100px'],
+                                  rotate: ['0deg', '45deg'],
+                                  transform: ['translate(20px)',
+                                              'translate(30px)'],
+                                  offsetDistance: ['0%', '100%'] },
+                                100 * MS_PER_SEC);
+
+  div.style.setProperty('translate', '50px', 'important');
+  getComputedStyle(div).translate;
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Animation overridden by an !important rule reports that it is ' +
+    'NOT running on the compositor');
+
+  const properties = animation.effect.getProperties();
+  properties.forEach(property => {
+    assert_true(!property.runningOnCompositor,
+                property.property + ' is not running on the compositor');
+  });
+}, 'Multiple transform-like properties animation does not runs on the ' +
+   'compositor because one of the transform-like property is overridden ' +
+   'by an !important rule');
+
+// FIXME:  Bug 1593106: We should still run the animations on the compositor if
+// offset-* doesn't have any effect.
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ translate: ['0px', '100px'],
+                                  rotate: ['0deg', '45deg'],
+                                  transform: ['translate(0px)',
+                                              'translate(100px)'],
+                                  offsetDistance: ['0%', '100%'] },
+                                100 * MS_PER_SEC);
+
+  div.style.setProperty('offset-distance', '50%', 'important');
+  getComputedStyle(div).offsetDistance;
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_not_running_on_compositor(animation,
+    'Animation overridden by an !important rule reports that it is ' +
+    'NOT running on the compositor');
+
+  const properties = animation.effect.getProperties();
+  properties.forEach(property => {
+    assert_true(!property.runningOnCompositor,
+                property.property + ' is not running on the compositor');
+  });
+}, 'Multiple transform-like properties animation does not runs on the ' +
+   'compositor because one of the offset-* property is overridden ' +
+   'by an !important rule');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  const animation = div.animate({ rotate: ['0deg', '45deg'],
+                                  transform: ['translate(20px)',
+                                              'translate(30px)'],
+                                  offsetDistance: ['0%', '100%'] },
+                                100 * MS_PER_SEC);
+
+  div.style.setProperty('translate', '50px', 'important');
+  getComputedStyle(div).translate;
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'Animation is still running on the compositor');
+
+  const properties = animation.effect.getProperties();
+  properties.forEach(property => {
+    assert_true(property.runningOnCompositor,
+                property.property + ' is running on the compositor');
+  });
+}, 'Multiple transform-like properties animation still runs on the ' +
+   'compositor because the overridden-by-!important property does not have ' +
+   'animation');
+
+promise_test(async t => {
+  // We should run the animations on the compositor for this case:
+  // 1. A transition of 'translate'
+  // 2. An !important rule on 'translate'
+  // 3. An animation of 'scale'
+  const div = addDiv(t, { style: 'translate: 100px !important;' });
+  const animation = div.animate({ rotate: ['0deg', '45deg'] },
+                                100 * MS_PER_SEC);
+  div.style.transition = 'translate 100s';
+  getComputedStyle(div).transition;
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'rotate animation should be running on the compositor');
+
+  div.style.setProperty('translate', '200px', 'important');
+  getComputedStyle(div).translate;
+
+  const anims = div.getAnimations();
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(anims[0],
+    `${anims[0].effect.getProperties()[0].property} animation should be ` +
+    `running on the compositor`);
+  assert_animation_is_running_on_compositor(anims[1],
+    `${anims[1].effect.getProperties()[0].property} animation should be ` +
+    `running on the compositor`);
+}, 'Transform-like animations and transitions still runs on the compositor ' +
+   'because the !important rule is overridden by a transition, and the ' +
+   'transition property does not have animations');
+
+promise_test(async t => {
+  const container = addDiv(t, { style: 'transform-style: preserve-3d;' });
+  const targetA = addDiv(t, { style: 'transform-style: preserve-3d' });
+  const targetB = addDiv(t, { style: 'transform-style: preserve-3d' });
+  const targetC = addDiv(t);
+  container.appendChild(targetA);
+  targetA.append(targetB);
+  targetB.append(targetC);
+
+  const animation1 = targetA.animate({ rotate: ['0 0 1 0deg', '1 1 1 45deg'] },
+                                     100 * MS_PER_SEC);
+
+  const animation2 = targetC.animate({ rotate: ['0 0 1 0deg', '0 1 1 100deg'] },
+                                     100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation1);
+  await waitForAnimationReadyToRestyle(animation2);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation1,
+    'rotate animation in the 3d rendering context should be running on the ' +
+    'compositor');
+  assert_animation_is_running_on_compositor(animation2,
+    'rotate animation in the 3d rendering context should be running on the ' +
+    'compositor');
+}, 'Transform-like animations in the 3d rendering context should runs on the ' +
+   'compositor');
+
+promise_test(async t => {
+  const container = addDiv(t, { style: 'transform-style: preserve-3d;' });
+  const target = addDiv(t, { style: 'transform-style: preserve-3d;' });
+  const innerA = addDiv(t, { style: 'width: 50px; height: 50px;' });
+  // The frame of innerB is too large, so this makes its ancenstors and children
+  // in the 3d context be not allowed the async animations.
+  const innerB = addDiv(t, { style: 'rotate: 0 1 1 100deg; ' +
+                                    'transform-style: preserve-3d; ' +
+                                    'text-indent: -9999em' });
+  const innerB2 = addDiv(t, { style: 'rotate: 0 1 1 45deg;' });
+  const innerBText = document.createTextNode("innerB");
+  container.appendChild(target);
+  target.appendChild(innerA);
+  target.appendChild(innerB);
+  innerB.appendChild(innerBText);
+  innerB.appendChild(innerB2);
+
+  const animation1 = target.animate({ rotate: ['0 0 1 0deg', '1 1 1 45deg'] },
+                                    100 * MS_PER_SEC);
+
+  const animation2 = innerA.animate({ rotate: ['0 0 1 0deg', '0 1 1 100deg'] },
+                                    100 * MS_PER_SEC);
+
+  const animation3 = innerB2.animate({ rotate: ['0 0 1 0deg', '0 1 1 90deg'] },
+                                     100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation1);
+  await waitForAnimationReadyToRestyle(animation2);
+  await waitForAnimationReadyToRestyle(animation3);
+  await waitForPaints();
+
+  const isPartialPrerenderEnabled =
+    SpecialPowers.getBoolPref('layout.animation.prerender.partial');
+
+  if (isPartialPrerenderEnabled) {
+    assert_animation_is_running_on_compositor(animation1,
+      'rotate animation in the 3d rendering context should be running on ' +
+      'the compositor even if one of its inner frames is too large');
+    assert_animation_is_running_on_compositor(animation2,
+      'rotate animation in the 3d rendering context is still running on ' +
+      'the compositor because its display item is created earlier');
+    assert_animation_is_running_on_compositor(animation3,
+      'rotate animation in the 3d rendering context should be running on ' +
+      'the compositor even if one of its parent frames is too large');
+  } else {
+    assert_animation_is_not_running_on_compositor(animation1,
+      'rotate animation in the 3d rendering context should not be running on ' +
+      'the compositor because one of its inner frames is too large');
+    assert_animation_is_running_on_compositor(animation2,
+      'rotate animation in the 3d rendering context is still running on ' +
+      'the compositor because its display item is created earlier');
+    assert_animation_is_not_running_on_compositor(animation3,
+      'rotate animation in the 3d rendering context should not be running on ' +
+      'the compositor because one of its parent frames is too large');
+  }
+  innerBText.remove();
+}, 'Transform-like animations in the 3d rendering context should run on ' +
+   'the compositor even if it is the ancestor of ones whose frames are too ' +
+   'large or its ancestor is not allowed to run on the compositor');
+
+promise_test(async t => {
+  const container = addDiv(t, { style: 'transform-style: preserve-3d;' });
+  const target = addDiv(t, { style: 'transform-style: preserve-3d;' });
+  // The frame of innerA is too large, so this makes its ancenstors and children
+  // in the 3d context be not allowed the async animations.
+  const innerA = addDiv(t, { style: 'transform-style: preserve-3d; ' +
+                                    'text-indent: -9999em' });
+  const innerAText = document.createTextNode("innerA");
+  const innerB = addDiv(t, { style: 'width: 50px; height: 50px;' });
+  container.appendChild(target);
+  target.appendChild(innerA);
+  target.appendChild(innerB);
+  innerA.appendChild(innerAText);
+
+  const animation1 = target.animate({ rotate: ['0 0 1 0deg', '1 1 1 45deg'] },
+                                    100 * MS_PER_SEC);
+
+  const animation2 = innerA.animate({ rotate: ['0 0 1 0deg', '0 1 1 100deg'] },
+                                    100 * MS_PER_SEC);
+
+  const animation3 = innerB.animate({ rotate: ['0 0 1 0deg', '0 1 1 90deg'] },
+                                    100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation1);
+  await waitForAnimationReadyToRestyle(animation2);
+  await waitForAnimationReadyToRestyle(animation3);
+  await waitForPaints();
+
+  const isPartialPrerenderEnabled =
+    SpecialPowers.getBoolPref('layout.animation.prerender.partial');
+
+  if (isPartialPrerenderEnabled) {
+    assert_animation_is_running_on_compositor(animation1,
+      'rotate animation in the 3d rendering context should be running on ' +
+      'the compositor even if one of its inner frames is too large');
+    assert_animation_is_running_on_compositor(animation2,
+      'rotate animation in the 3d rendering context should be running on ' +
+      'the compositor even if its frame size is too large');
+    assert_animation_is_running_on_compositor(animation3,
+      'rotate animation in the 3d rendering context should be running on ' +
+      'the compositor even if its previous sibling frame is too large');
+  } else {
+    assert_animation_is_not_running_on_compositor(animation1,
+      'rotate animation in the 3d rendering context should not be running on ' +
+      'the compositor because one of its inner frames is too large');
+    assert_animation_is_not_running_on_compositor(animation2,
+      'rotate animation in the 3d rendering context should not be running on ' +
+      'the compositor because its frame size is too large');
+    assert_animation_is_not_running_on_compositor(animation3,
+      'rotate animation in the 3d rendering context should not be running on ' +
+      'the compositor because its previous sibling frame is too large');
+  }
+  innerAText.remove();
+}, 'Transform-like animations in the 3d rendering context should run on ' +
+   'the compositor even if its previous sibling frame size is too large');
+
+</script>
+</body>
diff --git a/dom/animation/test/chrome/test_simulate_compute_values_failure.html b/dom/animation/test/chrome/test_simulate_compute_values_failure.html
new file mode 100644
index 0000000000..2ee041c9f8
--- /dev/null
+++ b/dom/animation/test/chrome/test_simulate_compute_values_failure.html
@@ -0,0 +1,371 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Bug 1276688 - Test for properties that parse correctly but which we fail
+       to convert to computed values</title>
+<script type="application/javascript" src="../testharness.js"></script>
+<script type="application/javascript" src="../testharnessreport.js"></script>
+<script type="application/javascript" src="../testcommon.js"></script>
+</head>
+<body>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1276688"
+  target="_blank">Mozilla Bug 1276688</a>
+<div id="log"></div>
+<script>
+'use strict';
+
+function assert_properties_equal(actual, expected) {
+  assert_equals(actual.length, expected.length);
+
+  var compareProperties = (a, b) =>
+    a.property == b.property ? 0 : (a.property < b.property ? -1 : 1);
+
+  var sortedActual   = actual.sort(compareProperties);
+  var sortedExpected = expected.sort(compareProperties);
+
+  // We want to serialize the values in the following form:
+  //
+  //  { offset: 0, easing: linear, composite: replace, value: 5px }, ...
+  //
+  // So that we can just compare strings and, in the failure case,
+  // easily see where the differences lie.
+  var serializeMember = value => {
+    return typeof value === 'undefined' ? '<not set>' : value;
+  }
+  var serializeValues = values =>
+    values.map(value =>
+      '{ ' +
+        [ 'offset', 'value', 'easing', 'composite' ].map(
+          member => `${member}: ${serializeMember(value[member])}`
+        ).join(', ') +
+      ' }')
+    .join(', ');
+
+  for (var i = 0; i < sortedActual.length; i++) {
+    assert_equals(sortedActual[i].property,
+                  sortedExpected[i].property,
+                  'CSS property name should match');
+    assert_equals(serializeValues(sortedActual[i].values),
+                  serializeValues(sortedExpected[i].values),
+                  `Values arrays do not match for `
+                  + `${sortedActual[i].property} property`);
+  }
+}
+
+// Shorthand for constructing a value object
+function value(offset, value, composite, easing) {
+  return { offset, value, easing, composite };
+}
+
+var gTests = [
+  // ---------------------------------------------------------------------
+  //
+  // Tests for properties that parse correctly but which we fail to
+  // convert to computed values.
+  //
+  // ---------------------------------------------------------------------
+
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' initial keyframe',
+    frames:   [ { margin: '5px', simulateComputeValuesFailure: true },
+                { margin: '5px' } ],
+    expected: [  ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' initial keyframe where we have enough values to create'
+              + ' a final segment',
+    frames:   [ { margin: '5px', simulateComputeValuesFailure: true },
+                { margin: '5px' },
+                { margin: '5px' } ],
+    expected: [  ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' initial overlapping keyframes (first in series of two)',
+    frames:   [ { margin: '5px', offset: 0,
+                  simulateComputeValuesFailure: true },
+                { margin: '5px', offset: 0 },
+                { margin: '5px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' initial overlapping keyframes (second in series of two)',
+    frames:   [ { margin: '5px', offset: 0 },
+                { margin: '5px', offset: 0,
+                  simulateComputeValuesFailure: true },
+                { margin: '5px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' initial overlapping keyframes (second in series of three)',
+    frames:   [ { margin: '5px', offset: 0 },
+                { margin: '5px', offset: 0,
+                  simulateComputeValuesFailure: true },
+                { margin: '5px', offset: 0 },
+                { margin: '5px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace'),
+                            value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace'),
+                            value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace'),
+                            value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace'),
+                            value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' final keyframe',
+    frames:   [ { margin: '5px' },
+                { margin: '5px', simulateComputeValuesFailure: true } ],
+    expected: [  ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' final keyframe where it forms the last segment in the series',
+    frames:   [ { margin: '5px' },
+                { margin: '5px',
+                  marginLeft: '5px',
+                  marginRight: '5px',
+                  marginBottom: '5px',
+                  // margin-top sorts last and only it will be missing since
+                  // the other longhand components are specified
+                  simulateComputeValuesFailure: true } ],
+    expected: [ { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' final keyframe where we have enough values to create'
+              + ' an initial segment',
+    frames:   [ { margin: '5px' },
+                { margin: '5px' },
+                { margin: '5px', simulateComputeValuesFailure: true } ],
+    expected: [  ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' final overlapping keyframes (first in series of two)',
+    frames:   [ { margin: '5px' },
+                { margin: '5px', offset: 1,
+                  simulateComputeValuesFailure: true },
+                { margin: '5px', offset: 1 } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' final overlapping keyframes (second in series of two)',
+    frames:   [ { margin: '5px' },
+                { margin: '5px', offset: 1 },
+                { margin: '5px', offset: 1,
+                  simulateComputeValuesFailure: true } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' final overlapping keyframes (second in series of three)',
+    frames:   [ { margin: '5px' },
+                { margin: '5px', offset: 1 },
+                { margin: '5px', offset: 1,
+                  simulateComputeValuesFailure: true },
+                { margin: '5px', offset: 1 } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace'),
+                            value(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' intermediate keyframe',
+    frames:   [ { margin: '5px' },
+                { margin: '5px', simulateComputeValuesFailure: true },
+                { margin: '5px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' initial keyframe along with other values',
+    // simulateComputeValuesFailure only applies to shorthands so we can set
+    // it on the same keyframe and it will only apply to |margin| and not
+    // |left|.
+    frames:   [ { margin: '77%', left: '10px',
+                  simulateComputeValuesFailure: true },
+                { margin: '5px', left: '20px' } ],
+    expected: [ { property: 'left',
+                  values: [ value(0, '10px', 'replace', 'linear'),
+                            value(1, '20px', 'replace') ] } ],
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' initial keyframe along with other values where those'
+              + ' values sort after the property with missing values',
+    frames:   [ { margin: '77%', right: '10px',
+                  simulateComputeValuesFailure: true },
+                { margin: '5px', right: '20px' } ],
+    expected: [ { property: 'right',
+                  values: [ value(0, '10px', 'replace', 'linear'),
+                            value(1, '20px', 'replace') ] } ],
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' final keyframe along with other values',
+    frames:   [ { margin: '5px', left: '10px' },
+                { margin: '5px', left: '20px',
+                  simulateComputeValuesFailure: true } ],
+    expected: [ { property: 'left',
+                  values: [ value(0, '10px', 'replace', 'linear'),
+                            value(1, '20px', 'replace') ] } ],
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' final keyframe along with other values where those'
+              + ' values sort after the property with missing values',
+    frames:   [ { margin: '5px', right: '10px' },
+                { margin: '5px', right: '20px',
+                  simulateComputeValuesFailure: true } ],
+    expected: [ { property: 'right',
+                  values: [ value(0, '10px', 'replace', 'linear'),
+                            value(1, '20px', 'replace') ] } ],
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' an intermediate keyframe along with other values',
+    frames:   [ { margin: '5px', left: '10px' },
+                { margin: '5px', left: '20px',
+                  simulateComputeValuesFailure: true },
+                { margin: '5px', left: '30px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'left',
+                  values: [ value(0,   '10px', 'replace', 'linear'),
+                            value(0.5, '20px', 'replace', 'linear'),
+                            value(1,   '30px', 'replace') ] } ]
+  },
+  { desc:     'a property that can\'t be resolved to computed values in'
+              + ' an intermediate keyframe by itself',
+    frames:   [ { margin: '5px', left: '10px' },
+                { margin: '5px',
+                  simulateComputeValuesFailure: true },
+                { margin: '5px', left: '30px' } ],
+    expected: [ { property: 'margin-top',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-right',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-bottom',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'margin-left',
+                  values: [ value(0, '5px', 'replace', 'linear'),
+                            value(1, '5px', 'replace') ] },
+                { property: 'left',
+                  values: [ value(0,   '10px', 'replace', 'linear'),
+                            value(1,   '30px', 'replace') ] } ]
+  },
+];
+
+setup({explicit_done: true});
+
+SpecialPowers.pushPrefEnv(
+  {
+    set: [
+      ["dom.animations-api.core.enabled", false],
+      ["dom.animations-api.implicit-keyframes.enabled", false],
+    ],
+  },
+  function() {
+    gTests.forEach(function(subtest) {
+      test(function(t) {
+        var div = addDiv(t);
+        var animation = div.animate(subtest.frames, 100 * MS_PER_SEC);
+        assert_properties_equal(
+          animation.effect.getProperties(),
+          subtest.expected
+        );
+      }, subtest.desc);
+    });
+
+    done();
+  }
+);
+</script>
+</body>
diff --git a/dom/animation/test/crashtests/1134538.html b/dom/animation/test/crashtests/1134538.html
new file mode 100644
index 0000000000..136d63deee
--- /dev/null
+++ b/dom/animation/test/crashtests/1134538.html
@@ -0,0 +1,8 @@
+<!doctype html>
+<div contenteditable=true style="transition-property: width;"></div>
+<style>
+html {
+  transition-delay: 18446744073709551584s;
+  transform: rotate(0deg);
+}
+</style>
diff --git a/dom/animation/test/crashtests/1216842-1.html b/dom/animation/test/crashtests/1216842-1.html
new file mode 100644
index 0000000000..6ac40b2fb8
--- /dev/null
+++ b/dom/animation/test/crashtests/1216842-1.html
@@ -0,0 +1,35 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <title>Bug 1216842: effect-level easing function produces negative values (compositor thread)</title>
+    <style>
+    #target {
+      width: 100px; height: 100px;
+      background: blue;
+    }
+    </style>
+  </head>
+  <body>
+  <div id="target"></div>
+  </body>
+  <script>
+    var target = document.getElementById("target");
+    var effect =
+      new KeyframeEffect(
+        target,
+        { opacity: [0, 1] },
+        {
+          fill: "forwards",
+          /* The function produces negative values in (0, 0.766312060) */
+          easing: "cubic-bezier(0,-0.5,1,-0.5)",
+          duration: 100,
+          iterations: 0.75 /* To finish in the extraporation range */
+        }
+      );
+    var animation = new Animation(effect, document.timeline);
+    animation.play();
+    animation.finished.then(function() {
+      document.documentElement.className = "";
+    });
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1216842-2.html b/dom/animation/test/crashtests/1216842-2.html
new file mode 100644
index 0000000000..7bae8a3116
--- /dev/null
+++ b/dom/animation/test/crashtests/1216842-2.html
@@ -0,0 +1,35 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <title>Bug 1216842: effect-level easing function produces values greater than 1 (compositor thread)</title>
+    <style>
+    #target {
+      width: 100px; height: 100px;
+      background: blue;
+    }
+    </style>
+  </head>
+  <body>
+  <div id="target"></div>
+  </body>
+  <script>
+    var target = document.getElementById("target");
+    var effect =
+      new KeyframeEffect(
+        target,
+        { opacity: [0, 1] },
+        {
+          fill: "forwards",
+          /* The function produces values greater than 1 in (0.23368794, 1) */
+          easing: "cubic-bezier(0,1.5,1,1.5)",
+          duration: 100,
+          iterations: 0.25 /* To finish in the extraporation range */
+        }
+      );
+    var animation = new Animation(effect, document.timeline);
+    animation.play();
+    animation.finished.then(function() {
+      document.documentElement.className = "";
+    });
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1216842-3.html b/dom/animation/test/crashtests/1216842-3.html
new file mode 100644
index 0000000000..1bc2179a86
--- /dev/null
+++ b/dom/animation/test/crashtests/1216842-3.html
@@ -0,0 +1,27 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <title>Bug 1216842: effect-level easing function produces values greater than 1 (main-thread)</title>
+  </head>
+  <body>
+  <div id="target"></div>
+  </body>
+  <script>
+    var target = document.getElementById("target");
+    var effect =
+      new KeyframeEffect(
+        target,
+        { color: ["red", "blue"] },
+        {
+          fill: "forwards",
+          /* The function produces values greater than 1 in (0.23368794, 1) */
+          easing: "cubic-bezier(0,1.5,1,1.5)",
+          duration: 100
+        }
+      );
+    var animation = new Animation(effect, document.timeline);
+    animation.pause();
+    animation.currentTime = 250;
+    document.documentElement.className = "";
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1216842-4.html b/dom/animation/test/crashtests/1216842-4.html
new file mode 100644
index 0000000000..eba13c396a
--- /dev/null
+++ b/dom/animation/test/crashtests/1216842-4.html
@@ -0,0 +1,27 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <title>Bug 1216842: effect-level easing function produces negative values (main-thread)</title>
+  </head>
+  <body>
+  <div id="target"></div>
+  </body>
+  <script>
+    var target = document.getElementById("target");
+    var effect =
+      new KeyframeEffect(
+        target,
+        { color: ["red", "blue"] },
+        {
+          fill: "forwards",
+          /* The function produces negative values in (0, 0.766312060) */
+          easing: "cubic-bezier(0,-0.5,1,-0.5)",
+          duration: 100
+        }
+      );
+    var animation = new Animation(effect, document.timeline);
+    animation.pause();
+    animation.currentTime = 250;
+    document.documentElement.className = "";
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1216842-5.html b/dom/animation/test/crashtests/1216842-5.html
new file mode 100644
index 0000000000..73b6f22c4b
--- /dev/null
+++ b/dom/animation/test/crashtests/1216842-5.html
@@ -0,0 +1,38 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <title>
+      Bug 1216842: effect-level easing function produces negative values passed
+      to step-end function (compositor thread)
+    </title>
+    <style>
+    #target {
+      width: 100px; height: 100px;
+      background: blue;
+    }
+    </style>
+  </head>
+  <body>
+  <div id="target"></div>
+  </body>
+  <script>
+    var target = document.getElementById("target");
+    var effect =
+      new KeyframeEffect(
+        target,
+        { opacity: [0, 1], easing: "step-end" },
+        {
+          fill: "forwards",
+          /* The function produces negative values in (0, 0.766312060) */
+          easing: "cubic-bezier(0,-0.5,1,-0.5)",
+          duration: 100,
+          iterations: 0.75 /* To finish in the extraporation range */
+        }
+      );
+    var animation = new Animation(effect, document.timeline);
+    animation.play();
+    animation.finished.then(function() {
+      document.documentElement.className = "";
+    });
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1216842-6.html b/dom/animation/test/crashtests/1216842-6.html
new file mode 100644
index 0000000000..aaf80eeec3
--- /dev/null
+++ b/dom/animation/test/crashtests/1216842-6.html
@@ -0,0 +1,38 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <title>
+      Bug 1216842: effect-level easing function produces values greater than 1
+      which are passed to step-end function (compositor thread)
+    </title>
+    <style>
+    #target {
+      width: 100px; height: 100px;
+      background: blue;
+    }
+    </style>
+  </head>
+  <body>
+  <div id="target"></div>
+  </body>
+  <script>
+    var target = document.getElementById("target");
+    var effect =
+      new KeyframeEffect(
+        target,
+        { opacity: [0, 1], easing: "step-end" },
+        {
+          fill: "forwards",
+          /* The function produces values greater than 1 in (0.23368794, 1) */
+          easing: "cubic-bezier(0,1.5,1,1.5)",
+          duration: 100,
+          iterations: 0.25 /* To finish in the extraporation range */
+        }
+      );
+    var animation = new Animation(effect, document.timeline);
+    animation.play();
+    animation.finished.then(function() {
+      document.documentElement.className = "";
+    });
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1239889-1.html b/dom/animation/test/crashtests/1239889-1.html
new file mode 100644
index 0000000000..aa10ff3ab8
--- /dev/null
+++ b/dom/animation/test/crashtests/1239889-1.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <title>Bug 1239889</title>
+  </head>
+  <body>
+  </body>
+  <script>
+    var div = document.createElement('div');
+    var effect = new KeyframeEffect(div, { opacity: [0, 1] });
+    requestAnimationFrame(() => {
+      document.body.appendChild(div);
+      document.documentElement.classList.remove("reftest-wait");
+    });
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1244595-1.html b/dom/animation/test/crashtests/1244595-1.html
new file mode 100644
index 0000000000..13b2e2d7e7
--- /dev/null
+++ b/dom/animation/test/crashtests/1244595-1.html
@@ -0,0 +1,3 @@
+<div id=target><script>
+  var player = target.animate([{background: 'green'}, {background: 'green'}]);
+</script>
diff --git a/dom/animation/test/crashtests/1272475-1.html b/dom/animation/test/crashtests/1272475-1.html
new file mode 100644
index 0000000000..e0b0495388
--- /dev/null
+++ b/dom/animation/test/crashtests/1272475-1.html
@@ -0,0 +1,20 @@
+<!doctype html>
+<html>
+  <head>
+    <title>Bug 1272475 - scale function with an extreme large value</title>
+  <script>
+    function test() {
+      var div = document.createElement("div");
+      div.setAttribute("style", "width: 1px; height: 1px; " +
+                                "background: red;");
+      document.body.appendChild(div);
+      div.animate([ { "transform": "scale(8)" },
+                    { "transform": "scale(9.5e+307)" },
+                    { "transform": "scale(32)" } ],
+                  { "duration": 1000, "fill": "both" });
+    }
+  </script>
+  </head>
+  <body onload="test()">
+  </body>
+</html>
diff --git a/dom/animation/test/crashtests/1272475-2.html b/dom/animation/test/crashtests/1272475-2.html
new file mode 100644
index 0000000000..da0e8605bd
--- /dev/null
+++ b/dom/animation/test/crashtests/1272475-2.html
@@ -0,0 +1,20 @@
+<!doctype html>
+<html>
+  <head>
+    <title>Bug 1272475 - rotate function with an extreme large value</title>
+  <script>
+    function test() {
+      var div = document.createElement("div");
+      div.setAttribute("style", "width: 100px; height: 100px; " +
+                                "background: red;");
+      document.body.appendChild(div);
+      div.animate([ { "transform": "rotate(8rad)" },
+                    { "transform": "rotate(9.5e+307rad)" },
+                    { "transform": "rotate(32rad)" } ],
+                  { "duration": 1000, "fill": "both" });
+    }
+  </script>
+  </head>
+  <body onload="test()">
+  </body>
+</html>
diff --git a/dom/animation/test/crashtests/1277272-1-inner.html b/dom/animation/test/crashtests/1277272-1-inner.html
new file mode 100644
index 0000000000..2565aa6eb8
--- /dev/null
+++ b/dom/animation/test/crashtests/1277272-1-inner.html
@@ -0,0 +1,19 @@
+<!doctype html>
+<head>
+<script>
+function start() {
+  var animation = document.body.animate([{marks: 'crop'},{marks: 'crop'}], 12);
+  document.write('<html><body></body></html>');
+
+  setTimeout(function() { animation.play(); }, 4);
+  setTimeout(function() {
+    animation.timeline = undefined;
+
+    SpecialPowers.Cu.forceGC();
+    window.top.continueTest();
+  }, 5);
+}
+</script>
+</head>
+<body onload="start()"></body>
+</html>
diff --git a/dom/animation/test/crashtests/1277272-1.html b/dom/animation/test/crashtests/1277272-1.html
new file mode 100644
index 0000000000..71b6c24148
--- /dev/null
+++ b/dom/animation/test/crashtests/1277272-1.html
@@ -0,0 +1,25 @@
+<!doctype html>
+<html class="reftest-wait">
+<head>
+<script>
+var count = 0;
+
+function start() {
+  if (++count > 10) {
+    document.documentElement.className = "";
+    return;
+  }
+
+  var frame = document.getElementById("frame");
+  frame.src = "./1277272-1-inner.html";
+}
+
+function continueTest() {
+  setTimeout(start.bind(window), 1);
+}
+
+</script>
+</head>
+<body onload="start()"></body>
+<iframe id="frame">
+</html>
diff --git a/dom/animation/test/crashtests/1278485-1.html b/dom/animation/test/crashtests/1278485-1.html
new file mode 100644
index 0000000000..e7347f5d84
--- /dev/null
+++ b/dom/animation/test/crashtests/1278485-1.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+
+function boom()
+{
+  document.body.animate([],
+                        { duration: 6,
+                          easing: "cubic-bezier(0, -1e+39, 0, 0)" });
+  document.body.animate([],
+                        { duration: 6,
+                          easing: "cubic-bezier(0, 1e+39, 0, 0)" });
+  document.body.animate([],
+                        { duration: 6,
+                          easing: "cubic-bezier(0, 0, 0, -1e+39)" });
+  document.body.animate([],
+                        { duration: 6,
+                          easing: "cubic-bezier(0, 0, 0, 1e+39)" });
+}
+
+</script>
+</head>
+<body onload="boom();"></body>
+</html>
diff --git a/dom/animation/test/crashtests/1282691-1.html b/dom/animation/test/crashtests/1282691-1.html
new file mode 100644
index 0000000000..ab6e1a26c0
--- /dev/null
+++ b/dom/animation/test/crashtests/1282691-1.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html class=reftest-wait>
+<meta charset=utf-8>
+<script>
+
+function boom() {
+  const div = document.createElement('div');
+  const anim = div.animate([{}], {});
+  document.documentElement.appendChild(div);
+  anim.pause();
+  document.documentElement.removeChild(div);
+
+  requestAnimationFrame(() => {
+    document.documentElement.appendChild(div);
+    anim.play();
+    document.documentElement.className = '';
+  });
+}
+
+</script>
+</head>
+<body onload="boom();"></body>
+</html>
diff --git a/dom/animation/test/crashtests/1291413-1.html b/dom/animation/test/crashtests/1291413-1.html
new file mode 100644
index 0000000000..691a746c6e
--- /dev/null
+++ b/dom/animation/test/crashtests/1291413-1.html
@@ -0,0 +1,20 @@
+<!doctype html>
+<html class=reftest-wait>
+<script>
+window.onload = () => {
+  const div = document.createElement('div');
+
+  document.documentElement.appendChild(div);
+  const anim = div.animate([], 1000);
+
+  anim.ready.then(() => {
+    anim.pause();
+    anim.reverse();
+    anim.playbackRate = 0;
+    anim.ready.then(() => {
+      document.documentElement.className = '';
+    });
+  });
+};
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1291413-2.html b/dom/animation/test/crashtests/1291413-2.html
new file mode 100644
index 0000000000..fca3a93800
--- /dev/null
+++ b/dom/animation/test/crashtests/1291413-2.html
@@ -0,0 +1,21 @@
+<!doctype html>
+<html class=reftest-wait>
+<script>
+window.onload = () => {
+  const div = document.createElement('div');
+
+  document.documentElement.appendChild(div);
+  const anim = div.animate([], 1000);
+
+  anim.ready.then(() => {
+    anim.pause();
+    anim.reverse();
+    anim.playbackRate = 0;
+    anim.playbackRate = 1;
+    anim.ready.then(() => {
+      document.documentElement.className = '';
+    });
+  });
+};
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1304886-1.html b/dom/animation/test/crashtests/1304886-1.html
new file mode 100644
index 0000000000..703ef902b9
--- /dev/null
+++ b/dom/animation/test/crashtests/1304886-1.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html>
+<script>
+window.onload=function(){
+  var e = document.createElement("div");
+  document.documentElement.appendChild(e);
+  e.animate([{"font":"status-bar"},
+             {"font":"unset"}],
+            {duration:6,
+             iterationStart:4,
+             iterationComposite:"accumulate"});
+};
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1309198-1.html b/dom/animation/test/crashtests/1309198-1.html
new file mode 100644
index 0000000000..7fad5782c0
--- /dev/null
+++ b/dom/animation/test/crashtests/1309198-1.html
@@ -0,0 +1,40 @@
+<script>
+function start() {
+  o53=document.createElement('frameset');
+  o254=document.createElement('iframe');
+  o280=document.createElement('audio');
+  o317=document.documentElement;
+  o508=document.createElement('li');
+  o508.appendChild(o317);
+  o590=document.createElement('li');
+  o594=document.createElement('track');
+  o280.appendChild(o594);
+  o647=document.createElement('ol');
+  o654=document.createElement('li');
+  o647.appendChild(o654);
+  o654.insertAdjacentHTML('beforebegin','<iframe>');
+  document.write('<html><body></body></html>');
+  o955=document.documentElement;
+  document.documentElement.appendChild(o647);
+  o590.appendChild(o955);
+  document.close();
+  document.write('<html><body></body></html>');
+  document.documentElement.appendChild(o590);
+  document.documentElement.appendChild(o254);
+  o280.controls^=1;
+  SpecialPowers.forceGC();
+  o317.insertAdjacentHTML('afterend','<iframe>');
+  document.documentElement.appendChild(o280);
+  o2695=document.implementation.createHTMLDocument();
+  o2695.body.appendChild(o254);
+  o53.onerror=f0;
+  document.documentElement.appendChild(o508);
+  o2803=frames[1].document;
+  o2803.getAnimations();
+}
+function f0() {
+  o2803.write('<html><body></body></html>');
+  SpecialPowers.forceCC();
+}
+</script>
+<body onload="start()"></body>
diff --git a/dom/animation/test/crashtests/1322291-1.html b/dom/animation/test/crashtests/1322291-1.html
new file mode 100644
index 0000000000..87def99ba8
--- /dev/null
+++ b/dom/animation/test/crashtests/1322291-1.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<script>
+document.addEventListener("DOMContentLoaded", boom);
+function boom(){
+  let o1 = (function(){
+    let e=document.createElement("frameset");
+    document.documentElement.appendChild(e);
+    return e;
+  })();
+  let a1 = o1.animate({ "transform": "rotate3d(22,73,26,374grad)" },
+                      { duration: 10, delay: 100 });
+
+  // We need to wait the end of the delay to ensure that the animation is
+  // composited on the compositor, but there is no event for script animation
+  // that fires after the delay phase finished. So we wait for finished promise
+  // instead.
+  a1.finished.then(function() {
+    document.documentElement.className = "";
+  });
+}
+</script>
+</body>
+</html>
diff --git a/dom/animation/test/crashtests/1322291-2.html b/dom/animation/test/crashtests/1322291-2.html
new file mode 100644
index 0000000000..b93d53224d
--- /dev/null
+++ b/dom/animation/test/crashtests/1322291-2.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<style>
+div {
+  width: 100px;
+  height: 100px;
+  background-color: red;
+}
+</style>
+<body>
+<div id=o_0></div>
+<script>
+function boom(){
+  var anim = o_0.animate([
+    {},
+    {"transform": "scale(2)"},
+    {"transform": "none"}
+    ], {
+      duration: 100,
+      iterationStart: 0.5,
+    });
+  // We need to wait for finished promise just like we do in 1322291-1.html.
+  anim.finished.then(function() {
+    document.documentElement.classList.remove("reftest-wait");
+  });
+}
+document.addEventListener("DOMContentLoaded", boom);
+</script>
+
+</body>
+</html>
diff --git a/dom/animation/test/crashtests/1322382-1.html b/dom/animation/test/crashtests/1322382-1.html
new file mode 100644
index 0000000000..6ca9c1b836
--- /dev/null
+++ b/dom/animation/test/crashtests/1322382-1.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<style>
+details {
+  background-color: blue;
+  width: 100px;
+  height: 100px;
+}
+</style>
+<html>
+<details id=o1><div></div></details>
+<script>
+window.onload = function(){
+  o1.animate([{'transform': 'none'}], 100);
+};
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1323114-1.html b/dom/animation/test/crashtests/1323114-1.html
new file mode 100644
index 0000000000..344fd87db0
--- /dev/null
+++ b/dom/animation/test/crashtests/1323114-1.html
@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html>
+<body>
+<div id=a />
+<script>
+addEventListener("DOMContentLoaded", function(){
+  a.animate([{"transform": "matrix3d(25,8788,-69,-24,-3,85,52,3,63,0,12,36810,-68,15,82,0) rotate(77rad)"}],
+             {fill: "both", iterationStart: 45, iterationComposite: "accumulate"});
+});
+</script>
+</body>
+</html>
diff --git a/dom/animation/test/crashtests/1323114-2.html b/dom/animation/test/crashtests/1323114-2.html
new file mode 100644
index 0000000000..527d05effa
--- /dev/null
+++ b/dom/animation/test/crashtests/1323114-2.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<style>
+div {
+  width: 100px;
+  height: 100px;
+  background-color: blue;
+  transform: rotate(45deg);
+}
+</style>
+<div id="div"></div>
+<script>
+addEventListener('DOMContentLoaded', function (){
+  var target = document.getElementById('div');
+  target.animate([{ transform: 'translateX(100px)', composite: 'accumulate' },
+                  { transform: 'none' }],
+                 1000);
+});
+</script>
diff --git a/dom/animation/test/crashtests/1323119-1.html b/dom/animation/test/crashtests/1323119-1.html
new file mode 100644
index 0000000000..fd979822b8
--- /dev/null
+++ b/dom/animation/test/crashtests/1323119-1.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<body>
+<script>
+addEventListener("DOMContentLoaded", function() {
+  let a = document.createElement("th");
+  document.documentElement.appendChild(a);
+  a.animate([{"mask": "repeat-y "}], 484);
+  document.documentElement.classList.remove("reftest-wait");
+});
+</script>
+</body>
+</html>
diff --git a/dom/animation/test/crashtests/1324554-1.html b/dom/animation/test/crashtests/1324554-1.html
new file mode 100644
index 0000000000..b3f9435a18
--- /dev/null
+++ b/dom/animation/test/crashtests/1324554-1.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+  <head>
+  <meta charset="UTF-8">
+  <title>Bug 1324554 - missing final keyframes and zero-length segments together</title>
+  </head>
+  <script>
+    function go() {
+      var div = document.getElementById('target');
+      div.animate([ { "flex": "none" },
+                    { "flex": "initial", offset: 0.5 },
+                    { "flex": "0.0 ", offset: 0.5 },
+                    {} ]);
+    }
+  </script>
+  <body onload="go()">
+    <div id='target' ></div>
+  </body>
+</html>
diff --git a/dom/animation/test/crashtests/1325193-1.html b/dom/animation/test/crashtests/1325193-1.html
new file mode 100644
index 0000000000..bd0666497c
--- /dev/null
+++ b/dom/animation/test/crashtests/1325193-1.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<head>
+<meta charset="UTF-8">
+<script>
+function boom(){
+  o_0.animate([{"perspective": "262ex"}, {}], {duration: 1070, iterationStart: 68, iterationComposite: "accumulate"});
+  o_0.animate([{"color": "white", "flex": "inherit"}, {"color": "red", "flex": "66% "}], 3439);
+  o_0.animate([{"font": "icon"}], 1849);
+  setTimeout(function() {
+    document.documentElement.classList.remove("reftest-wait");
+  }, 500);
+}
+document.addEventListener("DOMContentLoaded", boom);
+</script>
+</head>
+<body><details id=o_0><q></q></details></body>
+</html>
diff --git a/dom/animation/test/crashtests/1330190-1.html b/dom/animation/test/crashtests/1330190-1.html
new file mode 100644
index 0000000000..fa14e0f741
--- /dev/null
+++ b/dom/animation/test/crashtests/1330190-1.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<span id=a />
+<script>
+addEventListener("DOMContentLoaded", function(){
+  a.animate([{"left": "38%"}], 100);
+  a.appendChild(document.createElement("div"));
+  document.documentElement.classList.remove("reftest-wait");
+});
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1330190-2.html b/dom/animation/test/crashtests/1330190-2.html
new file mode 100644
index 0000000000..57e5d31b28
--- /dev/null
+++ b/dom/animation/test/crashtests/1330190-2.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<head>
+<style>
+@keyframes anim {
+}
+
+#o_0:before {
+  animation: anim 10s;
+  content: "";
+}
+</style>
+<meta charset="UTF-8">
+<script>
+function boom(){
+  function getPseudoElement() {
+    var anim = document.getAnimations()[0];
+    anim.cancel();
+    return anim.effect.target;
+  }
+
+  var target = getPseudoElement();
+  target.animate([{"perspective": "262ex"}, {}], {duration: 1070, iterationStart: 68, iterationComposite: "accumulate"});
+  target.animate([{"color": "white", "flex": "inherit"}, {"color": "red", "flex": "66% "}], 3439);
+  target.animate([{"font": "icon"}], 1849);
+  setTimeout(function() {
+    document.documentElement.classList.remove("reftest-wait");
+  }, 500);
+}
+document.addEventListener("DOMContentLoaded", boom);
+</script>
+</head>
+<body>
+<div id=o_0></div>
+</body>
+</html>
diff --git a/dom/animation/test/crashtests/1330513-1.html b/dom/animation/test/crashtests/1330513-1.html
new file mode 100644
index 0000000000..a497cc9e27
--- /dev/null
+++ b/dom/animation/test/crashtests/1330513-1.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+<body id=a></body>
+<script>
+document.getElementById("a")
+  .animate([{"filter": "grayscale(28%)"}], {fill:"forwards", composite:"add"});
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1332588-1.html b/dom/animation/test/crashtests/1332588-1.html
new file mode 100644
index 0000000000..11719a86ca
--- /dev/null
+++ b/dom/animation/test/crashtests/1332588-1.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<head>
+<meta charset="UTF-8">
+<style>
+span {
+  width: 100px;
+  height: 100px;
+  background-color: red;
+}
+</style>
+<script>
+window.onload = function() {
+  let body = document.getElementsByTagName("body")[0];
+  let o_0 = document.createElement("span");
+  body.appendChild(o_0);
+  o_0.animate([{ "padding": "57pt", "transform": "none" },
+               { "padding": "57pt", "transform": "rotate(90deg)" }] , 10000);
+  body.appendChild(document.createElement("colgroup"));
+  document.documentElement.classList.remove("reftest-wait");
+};
+</script>
+</head>
+<body></body>
+</html>
diff --git a/dom/animation/test/crashtests/1333539-1.html b/dom/animation/test/crashtests/1333539-1.html
new file mode 100644
index 0000000000..c9111890b0
--- /dev/null
+++ b/dom/animation/test/crashtests/1333539-1.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<head>
+<meta charset="UTF-8">
+<script>
+window.onload = function(){
+  let body = document.getElementsByTagName("body")[0];
+  let target = document.createElement("div");
+  let anim1 = new Animation();
+  let anim2 = new Animation();
+  let effect = new KeyframeEffect(target, { opacity: [ 0, 1 ] }, 1000);
+  body.appendChild(target);
+  target.appendChild(document.createElement("meter"));
+  anim1.startTime = 88;
+  anim1.timeline = null;
+  anim1.pause();
+  anim1.effect = effect;
+  anim2.effect = effect;
+  anim1.effect = effect;
+
+  // anim1, since it doesn't have a timeline, will remain pause-pending,
+  // so just wait on anim2.
+  anim2.ready.then(() => {
+    document.documentElement.classList.remove("reftest-wait");
+  });
+};
+</script>
+</head>
+<body></body>
+</html>
diff --git a/dom/animation/test/crashtests/1333539-2.html b/dom/animation/test/crashtests/1333539-2.html
new file mode 100644
index 0000000000..b00700eccb
--- /dev/null
+++ b/dom/animation/test/crashtests/1333539-2.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<style>
+div {
+  width: 100px;
+  height: 100px;
+  background-color: blue;
+}
+</style>
+<script>
+window.onload = function(){
+  let body = document.getElementsByTagName("body")[0];
+  let target = document.createElement("div");
+  let anim1 = new Animation();
+  let anim2 = new Animation();
+  let effect = new KeyframeEffect(target, { opacity: [ 0, 1 ] }, 1000);
+  body.appendChild(target);
+  anim1.startTime = 88;
+  anim1.timeline = null;
+  anim1.pause();
+  anim1.effect = effect;
+  anim2.effect = effect;
+  anim1.effect = effect;
+  // Put another opacity animation on the top of the effect stack so that we
+  // try to send a lower priority animation that has no timeline to the
+  // compositor.
+  let anim3 = target.animate({ opacity : [ 1, 0 ] }, 1000);
+
+  Promise.all([anim1.ready, anim2.ready, anim2.ready]).then(function() {
+    document.documentElement.classList.remove("reftest-wait");
+  });
+};
+</script>
+</head>
+<body></body>
+</html>
diff --git a/dom/animation/test/crashtests/1334582-1.html b/dom/animation/test/crashtests/1334582-1.html
new file mode 100644
index 0000000000..d67ddc3c52
--- /dev/null
+++ b/dom/animation/test/crashtests/1334582-1.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+window.onload = function(){
+  let a = document.documentElement.animate([], {"iterations": 1.7976931348623157e+308, "fill": "both"});
+};
+</script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1334582-2.html b/dom/animation/test/crashtests/1334582-2.html
new file mode 100644
index 0000000000..d3b223650d
--- /dev/null
+++ b/dom/animation/test/crashtests/1334582-2.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+window.onload = function(){
+  let a = document.documentElement.animate([], {"iterationStart": 1.7976931348623157e+308, "fill": "both"});
+};
+</script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1334583-1.html b/dom/animation/test/crashtests/1334583-1.html
new file mode 100644
index 0000000000..b4d4109f0d
--- /dev/null
+++ b/dom/animation/test/crashtests/1334583-1.html
@@ -0,0 +1,9 @@
+<div style="width: 200px; height: 200px; background: purple" id=div>
+</div>
+<script>
+const animation = div.animate(
+  [ { transform: "scale(1)" },
+    { transform: "scale(2)" } ],
+    { iterations: Infinity, duration: 512 } );
+animation.currentTime = 2147483647;
+</script>
diff --git a/dom/animation/test/crashtests/1335998-1.html b/dom/animation/test/crashtests/1335998-1.html
new file mode 100644
index 0000000000..72353a9692
--- /dev/null
+++ b/dom/animation/test/crashtests/1335998-1.html
@@ -0,0 +1,28 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <title>
+      Bug 1335998 - Handle {Interpolate, Accumulate}Matrix of mismatched transform lists
+    </title>
+    <style>
+    #target {
+      width: 100px; height: 100px;
+      background: blue;
+      transform: rotate(45deg);
+    }
+    </style>
+  </head>
+  <body>
+  <div id="target"></div>
+  </body>
+  <script>
+    var div = document.getElementById("target");
+    var animation = div.animate([ { transform: 'translateX(200px) scale(2.0)',
+                                    composite: 'accumulate' },
+                                  { transform: 'rotate(-45deg)' } ],
+                                2000);
+    animation.finished.then(function() {
+      document.documentElement.className = "";
+    });
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1343589-1.html b/dom/animation/test/crashtests/1343589-1.html
new file mode 100644
index 0000000000..a494b83da3
--- /dev/null
+++ b/dom/animation/test/crashtests/1343589-1.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<head>
+<meta charset="UTF-8">
+<script>
+window.onload = function(){
+  let a = document.documentElement.animate(null,
+            { duration: 100, iterations: Number.POSITIVE_INFINITY });
+  a.startTime = 100000; // Set the start time far in the future
+  // Try reversing (this should throw because the target effect end is infinity)
+  try { a.reverse(); } catch(e) {}
+  // Do something that will trigger a timing update
+  a.effect.target = document.createElement("span");
+  document.documentElement.className = '';
+};
+</script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1359658-1.html b/dom/animation/test/crashtests/1359658-1.html
new file mode 100644
index 0000000000..972ec497fa
--- /dev/null
+++ b/dom/animation/test/crashtests/1359658-1.html
@@ -0,0 +1,33 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <meta charset=utf-8>
+    <title>Bug 1359658: Animation-only dirty descendants bit should be cleared
+           for display:none content</title>
+  </head>
+  <body>
+  <div id="ancestor">
+    <svg>
+      <rect id="target" width="100%" height="100%" fill="lime"/>
+    </svg>
+  </div>
+  </body>
+  <script>
+'use strict';
+
+const ancestor = document.getElementById('ancestor');
+const target   = document.getElementById('target');
+
+document.addEventListener('DOMContentLoaded', () => {
+  const animation = target.animate({ color: [ 'red', 'lime' ] },
+                                   { duration: 1000, iterations: Infinity });
+  requestAnimationFrame(() => {
+    // Tweak animation to cause animation dirty bit to be set
+    animation.effect.updateTiming({ duration: 2000 });
+    ancestor.style.display = "none";
+    getComputedStyle(ancestor).display;
+    document.documentElement.className = '';
+  });
+});
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1373712-1.html b/dom/animation/test/crashtests/1373712-1.html
new file mode 100644
index 0000000000..8b5c121c85
--- /dev/null
+++ b/dom/animation/test/crashtests/1373712-1.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>Bug 1373712 - Assertions of SpecifiedKeyframeArraysAreEqual(mKeyframes, keyframesCopy) with large color value
+</title>
+<meta charset="UTF-8">
+<script>
+document.documentElement.animate([{ "color": "hsl(63e292,41%,34%)" }]);
+</script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1379606-1.html b/dom/animation/test/crashtests/1379606-1.html
new file mode 100644
index 0000000000..89f756bf06
--- /dev/null
+++ b/dom/animation/test/crashtests/1379606-1.html
@@ -0,0 +1,21 @@
+<!doctype html>
+<style>
+div {
+  display: none;
+}
+</style>
+<div>
+<div>
+<div>
+<div>
+<div>
+<div id="target">
+</div>
+</div>
+</div>
+</div>
+</div>
+</div>
+<script>
+  target.animate({ color: "red" })
+</script>
diff --git a/dom/animation/test/crashtests/1393605-1.html b/dom/animation/test/crashtests/1393605-1.html
new file mode 100644
index 0000000000..9f282e58ba
--- /dev/null
+++ b/dom/animation/test/crashtests/1393605-1.html
@@ -0,0 +1,15 @@
+<!doctype html>
+<html>
+  <head>
+    <title>
+      Bug 1393605 - Still work if determinant of 2d matrix is not 1 or -1
+    </title>
+  </head>
+  <script>
+    document.documentElement.animate(
+      [ { 'transform': 'scale(4)' },
+        { 'transform': 'rotate(3grad) scaleX(0) ' +
+                       'translate(2mm) matrix(2,7,1,.32,7,0)' } ],
+      { fill: 'both' });
+  </script>
+</html>
diff --git a/dom/animation/test/crashtests/1400022-1.html b/dom/animation/test/crashtests/1400022-1.html
new file mode 100644
index 0000000000..8256091e1e
--- /dev/null
+++ b/dom/animation/test/crashtests/1400022-1.html
@@ -0,0 +1,10 @@
+<script>
+requestIdleCallback(function(){ location.reload() })
+a = document.createElement("x")
+document.documentElement.appendChild(a)
+b = document.createElement('link')
+b.setAttribute('rel', 'stylesheet')
+b.setAttribute('href', 'data:,*{border-block-start:solid}')
+document.head.appendChild(b)
+a.insertAdjacentHTML("afterBegin", "<d id='id0' style='transition-duration:1s'><svg filter='url(#id0)'>")
+</script>
diff --git a/dom/animation/test/crashtests/1401809.html b/dom/animation/test/crashtests/1401809.html
new file mode 100644
index 0000000000..7a3adcc60c
--- /dev/null
+++ b/dom/animation/test/crashtests/1401809.html
@@ -0,0 +1,14 @@
+<html>
+  <head>
+    <style></style>
+    <script>
+      o1 = document.createElement('t');
+      document.documentElement.appendChild(o1);
+      document.styleSheets[0].insertRule('* { will-change:an }', 0);
+      k = new KeyframeEffect(o1, [{'willChange':'s'}], {'':''});
+      k = null;
+      SpecialPowers.forceGC();
+      SpecialPowers.forceCC();
+    </script>
+  </head>
+</html>
diff --git a/dom/animation/test/crashtests/1411318-1.html b/dom/animation/test/crashtests/1411318-1.html
new file mode 100644
index 0000000000..5c8e7211c1
--- /dev/null
+++ b/dom/animation/test/crashtests/1411318-1.html
@@ -0,0 +1,15 @@
+<html>
+  <head>
+    <script>
+      o1 = (new DOMParser).parseFromString('', 'text/html');
+      o2 = document.createElement('canvas');
+      document.documentElement.appendChild(o2);
+      o3 = o2.animate([{'transform':'unset'}], {'delay':32});
+      o4 = o3.effect;
+      o5 = o1.createElement('d');
+      o6 = new Animation(o4, document.timeline);
+      o7 = o5.animate([], {});
+      o7.effect = o6.effect;
+    </script>
+  </head>
+</html>
diff --git a/dom/animation/test/crashtests/1467277-1.html b/dom/animation/test/crashtests/1467277-1.html
new file mode 100644
index 0000000000..c58fc64493
--- /dev/null
+++ b/dom/animation/test/crashtests/1467277-1.html
@@ -0,0 +1,6 @@
+<script>
+addEventListener("DOMContentLoaded", () => {
+  document.documentElement.animate(
+    [ { "transform": "rotate3d(1e58, 2, 6, 0turn)" } ], 1000)
+})
+</script>
diff --git a/dom/animation/test/crashtests/1468294-1.html b/dom/animation/test/crashtests/1468294-1.html
new file mode 100644
index 0000000000..e4092046ac
--- /dev/null
+++ b/dom/animation/test/crashtests/1468294-1.html
@@ -0,0 +1,7 @@
+<script>
+addEventListener("DOMContentLoaded", () => {
+  document.documentElement.animate([{ "transform": "matrix(2,1,1,5,2,8)" }],
+                                    { duration: 1000,
+                                      easing: "cubic-bezier(1,-15,.6,4)" });
+})
+</script>
diff --git a/dom/animation/test/crashtests/1524480-1.html b/dom/animation/test/crashtests/1524480-1.html
new file mode 100644
index 0000000000..89e5a412d9
--- /dev/null
+++ b/dom/animation/test/crashtests/1524480-1.html
@@ -0,0 +1,37 @@
+<!doctype html>
+<html class="reftest-wait">
+<meta charset=utf-8>
+<style>
+div {
+  display: none;
+  width: 100px;
+  height: 100px;
+  background: blue;
+}
+</style>
+<div id=div></div>
+<script>
+async function test() {
+  const animation = div.animate({ transform: ['none', 'none'] }, 1000);
+  animation.cancel();
+
+  await waitForFrame();
+
+  div.style.display = 'block';
+
+  await waitForFrame();
+  await waitForFrame();
+
+  animation.play();
+  await animation.finished;
+
+  document.documentElement.className = "";
+}
+
+function waitForFrame() {
+  return new Promise(resolve => requestAnimationFrame(resolve));
+}
+
+test();
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1575926.html b/dom/animation/test/crashtests/1575926.html
new file mode 100644
index 0000000000..cc37c94235
--- /dev/null
+++ b/dom/animation/test/crashtests/1575926.html
@@ -0,0 +1,24 @@
+<style>
+    @keyframes animation_0 {
+        88% { }
+    }
+
+    * {
+        animation-name: animation_0;
+        animation-delay: 4s;
+    }
+</style>
+<script>
+  function start () {
+    const input = document.createElement('input')
+    document.documentElement.appendChild(input)
+    const animations = input.getAnimations({})
+    const animation = animations[(3782796448 % animations.length)]
+    const effect = animation.effect
+    effect.setKeyframes({ 'borderLeft': ['inherit'] })
+    effect.target = null
+    input.contentEditable = 'true'
+  }
+
+  document.addEventListener('DOMContentLoaded', start)
+</script>
diff --git a/dom/animation/test/crashtests/1585770.html b/dom/animation/test/crashtests/1585770.html
new file mode 100644
index 0000000000..018d688582
--- /dev/null
+++ b/dom/animation/test/crashtests/1585770.html
@@ -0,0 +1,22 @@
+<html class="reftest-wait">
+<script>
+function start () {
+  const kf_effect =
+      new KeyframeEffect(document.documentElement,
+                         { opacity: ['', '1'] },
+                         { easing: 'step-end',
+                           duration: 10000 } );
+  const copy = new KeyframeEffect(kf_effect);
+  const animation = new Animation(copy);
+
+  animation.reverse();
+  document.documentElement.getBoundingClientRect();
+
+  requestAnimationFrame(() => {
+    document.documentElement.classList.remove("reftest-wait");
+  });
+}
+
+document.addEventListener('DOMContentLoaded', start);
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1604500-1.html b/dom/animation/test/crashtests/1604500-1.html
new file mode 100644
index 0000000000..01a6eafd1f
--- /dev/null
+++ b/dom/animation/test/crashtests/1604500-1.html
@@ -0,0 +1,24 @@
+<!doctype html>
+<html>
+<head>
+<script>
+function start () {
+  const keyframe = new KeyframeEffect(undefined, {});
+  const animation = new Animation(keyframe, undefined);
+  // Make animation run backwards...
+  animation.playbackRate = -100;
+  // But then set the current time to the future so it becomes "current"...
+  animation.currentTime = 2055;
+  // After updating the playback rate to zero, however, it should no longer
+  // be "current" (and this takes effect immediately because |animation| is
+  // paused)...
+  animation.updatePlaybackRate(0);
+  // Now update the target and hope nothing goes wrong...
+  keyframe.target = div;
+}
+
+document.addEventListener('DOMContentLoaded', start)
+</script>
+</head>
+<div id=div></div>
+</html>
diff --git a/dom/animation/test/crashtests/1611847.html b/dom/animation/test/crashtests/1611847.html
new file mode 100644
index 0000000000..720ce1179b
--- /dev/null
+++ b/dom/animation/test/crashtests/1611847.html
@@ -0,0 +1,23 @@
+<html>
+<head>
+  <style>
+    * {
+      transition-duration: 2s;
+    }
+  </style>
+  <script>
+    function start () {
+      const element = document.createElementNS('', 's');
+      const effect = new KeyframeEffect(document.documentElement, {}, 196);
+      document.documentElement.setAttribute('style', 'padding-left:3');
+      effect.updateTiming({ 'delay': 2723 });
+      const animations = document.getAnimations();
+      animations[0].effect = effect;
+      animations[0].updatePlaybackRate(-129);
+      effect.target = element;
+    }
+
+    document.addEventListener('DOMContentLoaded', start);
+  </script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1612891-1.html b/dom/animation/test/crashtests/1612891-1.html
new file mode 100644
index 0000000000..44cf022e88
--- /dev/null
+++ b/dom/animation/test/crashtests/1612891-1.html
@@ -0,0 +1,15 @@
+<html>
+<head>
+  <script>
+    function start() {
+      const element = document.createElement('img')
+      element.animate([
+        { 'easing': '' },
+        { 'offset': 'o' },
+      ], {})
+    }
+
+    window.addEventListener('load', start)
+  </script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1612891-2.html b/dom/animation/test/crashtests/1612891-2.html
new file mode 100644
index 0000000000..a9779ba70f
--- /dev/null
+++ b/dom/animation/test/crashtests/1612891-2.html
@@ -0,0 +1,15 @@
+<html>
+<head>
+  <script>
+    function start() {
+      const element = document.createElement('img')
+      element.animate([
+        { 'easing': '' },
+        123,
+      ], {})
+    }
+
+    window.addEventListener('load', start)
+  </script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1612891-3.html b/dom/animation/test/crashtests/1612891-3.html
new file mode 100644
index 0000000000..89e71b6ca8
--- /dev/null
+++ b/dom/animation/test/crashtests/1612891-3.html
@@ -0,0 +1,10 @@
+<html>
+<head>
+  <script>
+    document.addEventListener('DOMContentLoaded', () => {
+      const keyframe = new KeyframeEffect(document.documentElement, [{}], {})
+      keyframe.setKeyframes([{ 'easing': '' }, { 'offset': 'o', }])
+    })
+  </script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1633442.html b/dom/animation/test/crashtests/1633442.html
new file mode 100644
index 0000000000..cb4beedebc
--- /dev/null
+++ b/dom/animation/test/crashtests/1633442.html
@@ -0,0 +1,15 @@
+<!doctype html>
+<html class="reftest-wait">
+<head>
+<script>
+  document.addEventListener('DOMContentLoaded', () => {
+    document.documentElement.style.setProperty('transition-duration', '3s', '')
+    document.documentElement.style.setProperty('rotate', '2deg', undefined)
+    document.documentElement.style.setProperty('border-radius', '2%', '')
+    const [anim_1, anim_0] = document.documentElement.getAnimations({})
+    anim_1.effect = anim_0.effect
+    document.documentElement.classList.remove("reftest-wait");
+  })
+</script>
+</head>
+</html>
diff --git a/dom/animation/test/crashtests/1633486.html b/dom/animation/test/crashtests/1633486.html
new file mode 100644
index 0000000000..20b88f6327
--- /dev/null
+++ b/dom/animation/test/crashtests/1633486.html
@@ -0,0 +1,20 @@
+<!doctype html>
+<html>
+<head>
+  <script>
+    window.addEventListener('load', async () => {
+      const element = document.getElementById('target');
+      element.animate({
+        'all': ['initial']
+      }, {
+        'duration': 500,
+        'pseudoElement': '::marker',
+      })
+      element.hidden = false;
+    })
+  </script>
+</head>
+<ul>
+  <li id='target' hidden></li>
+</ul>
+</html>
diff --git a/dom/animation/test/crashtests/1656419.html b/dom/animation/test/crashtests/1656419.html
new file mode 100644
index 0000000000..4e76cb0a55
--- /dev/null
+++ b/dom/animation/test/crashtests/1656419.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<style>
+#target {
+  width: 200vw;
+  height: 200vh;
+}
+</style>
+<div id="target"></div>
+<script>
+const animA = target.animate(
+  { transform: 'translateX(100px)' },
+  { duration: 50 }
+);
+const animB = target.animate(
+  { transform: 'translateX(100px)', composite: 'add' },
+  { duration: 100 }
+);
+animB.finished.then(() => {
+  document.documentElement.classList.remove("reftest-wait");
+});
+</script>
+</html>
diff --git a/dom/animation/test/crashtests/1699890.html b/dom/animation/test/crashtests/1699890.html
new file mode 100644
index 0000000000..95aa1e190c
--- /dev/null
+++ b/dom/animation/test/crashtests/1699890.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+<style>
+@keyframes anim {
+  from { background-color: rgba(0, 0, 0, 0); }
+  to { background-color: rgba(255, 0, 0, 255); }
+}
+body {
+  animation: anim 100s;
+  width: 100vw;
+  height: 100vh;
+}
+</style>
diff --git a/dom/animation/test/crashtests/1706157.html b/dom/animation/test/crashtests/1706157.html
new file mode 100644
index 0000000000..cfa7b70b56
--- /dev/null
+++ b/dom/animation/test/crashtests/1706157.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <style>
+        @keyframes animation {
+            to {
+                left: 100px;
+            }
+        }
+        * {
+            animation: animation linear 1s;
+        }
+        #target {
+            animation-timing-function: steps(2965566999, jump-both);
+        }
+    </style>
+</head>
+<div id="target"></div>
+</html>
diff --git a/dom/animation/test/crashtests/1714421.html b/dom/animation/test/crashtests/1714421.html
new file mode 100644
index 0000000000..04099b55b7
--- /dev/null
+++ b/dom/animation/test/crashtests/1714421.html
@@ -0,0 +1,8 @@
+<script>
+document.addEventListener('DOMContentLoaded', () => {
+  document.documentElement.style.setProperty('scale', '89%', undefined)
+  document.documentElement.style.setProperty('-moz-transition-duration', '2009216159ms', '')
+  document.getAnimations()[0].timeline = undefined
+  document.documentElement.animate({'scale': ['none', 'none', 'none']}, 1807)
+})
+</script>
diff --git a/dom/animation/test/crashtests/1807966.html b/dom/animation/test/crashtests/1807966.html
new file mode 100644
index 0000000000..d2759d2b5c
--- /dev/null
+++ b/dom/animation/test/crashtests/1807966.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<style>
+  #target {
+    transition-timing-function: linear(calc(15 / 0), 10 10%);
+    transition-duration: 10s;
+  }
+</style>
+<script>
+  window.addEventListener('load', () => {
+    target.style.paddingBlock = "10px 10px";
+  })
+</script>
+<slot id="target"></slot>
diff --git a/dom/animation/test/crashtests/crashtests.list b/dom/animation/test/crashtests/crashtests.list
new file mode 100644
index 0000000000..6f5dd140e7
--- /dev/null
+++ b/dom/animation/test/crashtests/crashtests.list
@@ -0,0 +1,61 @@
+load 1134538.html
+pref(dom.animations-api.core.enabled,true) load 1239889-1.html
+load 1244595-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1216842-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1216842-2.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1216842-3.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1216842-4.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1216842-5.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1216842-6.html
+load 1272475-1.html
+load 1272475-2.html
+load 1278485-1.html
+pref(dom.animations-api.timelines.enabled,true) load 1277272-1.html
+load 1282691-1.html
+pref(dom.animations-api.core.enabled,true) load 1291413-1.html
+pref(dom.animations-api.core.enabled,true) load 1291413-2.html
+pref(dom.animations-api.compositing.enabled,true) load 1304886-1.html
+pref(dom.animations-api.getAnimations.enabled,true) load 1309198-1.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1322382-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.implicit-keyframes.enabled,true) load 1322291-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.implicit-keyframes.enabled,true) load 1322291-2.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) pref(dom.animations-api.compositing.enabled,true) load 1323114-1.html
+pref(dom.animations-api.compositing.enabled,true) load 1323114-2.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1323119-1.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1324554-1.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) pref(dom.animations-api.compositing.enabled,true) load 1325193-1.html
+load 1332588-1.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1330190-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.implicit-keyframes.enabled,true) pref(dom.animations-api.compositing.enabled,true) pref(dom.animations-api.getAnimations.enabled,true) load 1330190-2.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) pref(dom.animations-api.compositing.enabled,true) load 1330513-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1333539-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1333539-2.html
+load 1334582-1.html
+load 1334582-2.html
+load 1334583-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.compositing.enabled,true) load 1335998-1.html
+pref(dom.animations-api.core.enabled,true) load 1343589-1.html
+pref(dom.animations-api.core.enabled,true) load 1359658-1.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1373712-1.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1379606-1.html
+load 1393605-1.html
+load 1400022-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.implicit-keyframes.enabled,true) load 1401809.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.timelines.enabled,true) pref(dom.animations-api.implicit-keyframes.enabled,true) load 1411318-1.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1468294-1.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1467277-1.html
+load 1524480-1.html
+load 1575926.html
+pref(dom.animations-api.implicit-keyframes.enabled,true) load 1585770.html
+load 1604500-1.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.getAnimations.enabled,true) load 1611847.html
+pref(dom.animations-api.core.enabled,true) load 1612891-1.html
+pref(dom.animations-api.core.enabled,true) load 1612891-2.html
+pref(dom.animations-api.core.enabled,true) load 1612891-3.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.getAnimations.enabled,true) load 1633442.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.implicit-keyframes.enabled,true) load 1633486.html
+pref(layout.animation.prerender.partial,true) load 1656419.html
+pref(layout.css.step-position-jump.enabled,true) load 1706157.html
+pref(gfx.omta.background-color,true) load 1699890.html
+pref(dom.animations-api.core.enabled,true) pref(dom.animations-api.getAnimations.enabled,true) pref(dom.animations-api.timelines.enabled,true) load 1714421.html
+pref(layout.css.linear-easing-function.enabled,true) load 1807966.html
diff --git a/dom/animation/test/document-timeline/test_document-timeline.html b/dom/animation/test/document-timeline/test_document-timeline.html
new file mode 100644
index 0000000000..92a709e2f6
--- /dev/null
+++ b/dom/animation/test/document-timeline/test_document-timeline.html
@@ -0,0 +1,147 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Web Animations API: DocumentTimeline tests</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<iframe srcdoc='<html><meta charset=utf-8></html>' width="10" height="10" id="iframe"></iframe>
+<iframe srcdoc='<html style="display:none"><meta charset=utf-8></html>' width="10" height="10" id="hidden-iframe"></iframe>
+<div id="log"></div>
+<script>
+'use strict';
+
+test(function() {
+  assert_equals(document.timeline, document.timeline,
+    'document.timeline returns the same object every time');
+  var iframe = document.getElementById('iframe');
+  assert_not_equals(document.timeline, iframe.contentDocument.timeline,
+    'document.timeline returns a different object for each document');
+  assert_not_equals(iframe.contentDocument.timeline, null,
+    'document.timeline on an iframe is not null');
+},
+'document.timeline identity tests',
+{
+  help:   'http://dev.w3.org/fxtf/web-animations/#the-document-timeline',
+  assert: [ 'Each document has a timeline called the document timeline' ],
+  author: 'Brian Birtles'
+});
+
+async_test(function(t) {
+  const { AppConstants } = SpecialPowers.ChromeUtils.import(
+    "resource://gre/modules/AppConstants.jsm"
+  );
+
+  if (AppConstants.platform == "android") {
+    // Skip this test case on Android since it frequently fails on the
+    // environments. See bug 1761900.
+    t.done();
+  }
+
+  assert_greater_than_equal(document.timeline.currentTime, 0,
+    'document.timeline.currentTime is positive or zero');
+  // document.timeline.currentTime should be set even before document
+  // load fires. We expect this code to be run before document load and hence
+  // the above assertion is sufficient.
+  // If the following assertion fails, this test needs to be redesigned.
+  assert_true(document.readyState !== 'complete',
+    'Test is running prior to document load');
+
+  // Test that the document timeline's current time is measured from
+  // navigationStart.
+  //
+  // We can't just compare document.timeline.currentTime to
+  // window.performance.now() because currentTime is only updated on a sample
+  // so we use requestAnimationFrame instead.
+  window.requestAnimationFrame(t.step_func(function(rafTime) {
+    assert_equals(document.timeline.currentTime, rafTime,
+                  'document.timeline.currentTime matches' +
+                  ' requestAnimationFrame time');
+    t.done();
+  }));
+},
+'document.timeline.currentTime value tests',
+{
+  help: [
+    'http://dev.w3.org/fxtf/web-animations/#the-global-clock',
+    'http://dev.w3.org/fxtf/web-animations/#the-document-timeline'
+  ],
+  assert: [
+    'The global clock is a source of monotonically increasing time values',
+    'The time values of the document timeline are calculated as a fixed' +
+    ' offset from the global clock',
+    'the zero time corresponds to the navigationStart moment',
+    'the time value of each document timeline must be equal to the time ' +
+    'passed to animation frame request callbacks for that browsing context'
+  ],
+  author: 'Brian Birtles'
+});
+
+async_test(function(t) {
+  var valueAtStart = document.timeline.currentTime;
+  var timeAtStart = window.performance.now();
+  while (window.performance.now() - timeAtStart < 100) {
+    // Wait 100ms
+  }
+  assert_equals(document.timeline.currentTime, valueAtStart,
+    'document.timeline.currentTime does not change within a script block');
+  window.requestAnimationFrame(t.step_func(function() {
+    assert_true(document.timeline.currentTime > valueAtStart,
+      'document.timeline.currentTime increases between script blocks');
+    t.done();
+  }));
+},
+'document.timeline.currentTime liveness tests',
+{
+  help: 'http://dev.w3.org/fxtf/web-animations/#script-execution-and-live-updates-to-the-model',
+  assert: [ 'The value returned by the currentTime attribute of a' +
+            ' document timeline will not change within a script block' ],
+  author: 'Brian Birtles'
+});
+
+test(function() {
+  var hiddenIFrame = document.getElementById('hidden-iframe');
+  assert_equals(typeof hiddenIFrame.contentDocument.timeline.currentTime,
+    'number',
+    'currentTime of an initially hidden subframe\'s timeline is a number');
+  assert_true(hiddenIFrame.contentDocument.timeline.currentTime >= 0,
+    'currentTime of an initially hidden subframe\'s timeline is >= 0');
+}, 'document.timeline.currentTime hidden subframe test');
+
+async_test(function(t) {
+  var hiddenIFrame = document.getElementById('hidden-iframe');
+
+  // Don't run the test until after the iframe has completed loading or else the
+  // contentDocument may change.
+  var testToRunOnLoad = t.step_func(function() {
+    // Remove display:none
+    hiddenIFrame.style.display = 'block';
+    getComputedStyle(hiddenIFrame).display;
+
+    window.requestAnimationFrame(t.step_func(function() {
+      assert_greater_than(hiddenIFrame.contentDocument.timeline.currentTime, 0,
+        'document.timeline.currentTime is positive after removing'
+        + ' display:none');
+      var previousValue = hiddenIFrame.contentDocument.timeline.currentTime;
+
+      // Re-introduce display:none
+      hiddenIFrame.style.display = 'none';
+      getComputedStyle(hiddenIFrame).display;
+
+      window.requestAnimationFrame(t.step_func(function() {
+        assert_true(
+          hiddenIFrame.contentDocument.timeline.currentTime >= previousValue,
+          'document.timeline.currentTime does not go backwards after'
+          + ' re-setting display:none');
+        t.done();
+      }));
+    }));
+  });
+
+  if (hiddenIFrame.contentDocument.readyState === 'complete') {
+    testToRunOnLoad();
+  } else {
+    hiddenIFrame.addEventListener("load", testToRunOnLoad);
+  }
+}, 'document.timeline.currentTime hidden subframe dynamic test');
+
+</script>
diff --git a/dom/animation/test/document-timeline/test_request_animation_frame.html b/dom/animation/test/document-timeline/test_request_animation_frame.html
new file mode 100644
index 0000000000..3da4e4deb2
--- /dev/null
+++ b/dom/animation/test/document-timeline/test_request_animation_frame.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test RequestAnimationFrame Timestamps are monotonically increasing</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+<script>
+  var lastRequestAnimationFrameTimestamp = 0;
+  var requestAnimationFrameCount = 20;
+  var currentCount = 0;
+
+  // Test that all timestamps are always increasing
+  // and do not ever go backwards
+  function rafCallback(aTimestamp) {
+    SimpleTest.ok(aTimestamp > lastRequestAnimationFrameTimestamp,
+      "New RequestAnimationFrame timestamp should be later than the previous RequestAnimationFrame timestamp");
+    lastRequestAnimationFrameTimestamp = aTimestamp;
+    if (currentCount == requestAnimationFrameCount) {
+      SimpleTest.finish();
+    } else {
+      currentCount++;
+      window.requestAnimationFrame(rafCallback);
+    }
+  }
+
+  window.requestAnimationFrame(rafCallback);
+  SimpleTest.waitForExplicitFinish();
+</script>
diff --git a/dom/animation/test/mochitest.ini b/dom/animation/test/mochitest.ini
new file mode 100644
index 0000000000..bd4bfe8a61
--- /dev/null
+++ b/dom/animation/test/mochitest.ini
@@ -0,0 +1,81 @@
+[DEFAULT]
+prefs =
+  dom.animations-api.compositing.enabled=true
+  dom.animations-api.core.enabled=true
+  dom.animations-api.getAnimations.enabled=true
+  dom.animations-api.implicit-keyframes.enabled=true
+  dom.animations-api.timelines.enabled=true
+  gfx.omta.background-color=true
+  layout.css.motion-path.enabled=true
+  layout.css.individual-transform.enabled=true
+  layout.css.scroll-driven-animations.enabled=true
+  gfx.font_loader.delay=0
+# Support files for chrome tests that we want to load over HTTP need
+# to go in here, not chrome.ini.
+support-files =
+  chrome/file_animate_xrays.html
+  mozilla/xhr_doc.html
+  mozilla/file_deferred_start.html
+  mozilla/file_disable_animations_api_autoremove.html
+  mozilla/file_disable_animations_api_compositing.html
+  mozilla/file_disable_animations_api_get_animations.html
+  mozilla/file_disable_animations_api_implicit_keyframes.html
+  mozilla/file_disable_animations_api_timelines.html
+  mozilla/file_discrete_animations.html
+  mozilla/file_transition_finish_on_compositor.html
+  ../../../layout/style/test/property_database.js
+  testcommon.js
+  !/dom/events/test/event_leak_utils.js
+
+[document-timeline/test_document-timeline.html]
+[document-timeline/test_request_animation_frame.html]
+[mozilla/test_cascade.html]
+[mozilla/test_cubic_bezier_limits.html]
+[mozilla/test_deferred_start.html]
+skip-if = (os == 'win' && bits == 64) # Bug 1363957
+[mozilla/test_disable_animations_api_autoremove.html]
+[mozilla/test_disable_animations_api_compositing.html]
+[mozilla/test_disable_animations_api_get_animations.html]
+[mozilla/test_disable_animations_api_implicit_keyframes.html]
+[mozilla/test_disable_animations_api_timelines.html]
+[mozilla/test_disabled_properties.html]
+[mozilla/test_discrete_animations.html]
+[mozilla/test_distance_of_basic_shape.html]
+[mozilla/test_distance_of_filter.html]
+[mozilla/test_distance_of_path_function.html]
+[mozilla/test_distance_of_transform.html]
+[mozilla/test_document_timeline_origin_time_range.html]
+[mozilla/test_get_animations_on_scroll_animations.html]
+[mozilla/test_hide_and_show.html]
+[mozilla/test_mainthread_synchronization_pref.html]
+[mozilla/test_moz_prefixed_properties.html]
+[mozilla/test_pending_animation_tracker.html]
+[mozilla/test_restyles.html]
+support-files =
+  mozilla/file_restyles.html
+  mozilla/empty.html
+skip-if =
+  (os == 'android' && debug) #Bug 1784931
+  (os == 'linux' && tsan) #Bug 1784931
+  http3
+[mozilla/test_restyling_xhr_doc.html]
+[mozilla/test_set_easing.html]
+[mozilla/test_style_after_finished_on_compositor.html]
+[mozilla/test_transform_limits.html]
+[mozilla/test_transition_finish_on_compositor.html]
+skip-if = toolkit == 'android'
+[mozilla/test_underlying_discrete_value.html]
+[mozilla/test_unstyled.html]
+[mozilla/test_event_listener_leaks.html]
+skip-if = (os == "win" && processor == "aarch64") #bug 1535784
+[style/test_animation-seeking-with-current-time.html]
+[style/test_animation-seeking-with-start-time.html]
+[style/test_animation-setting-effect.html]
+[style/test_composite.html]
+skip-if = xorigin 
+[style/test_interpolation-from-interpolatematrix-to-none.html]
+[style/test_missing-keyframe.html]
+[style/test_missing-keyframe-on-compositor.html]
+skip-if =
+  fission && xorigin  # Bug 1716403 - New fission platform triage
+[style/test_transform-non-normalizable-rotate3d.html]
diff --git a/dom/animation/test/mozilla/empty.html b/dom/animation/test/mozilla/empty.html
new file mode 100644
index 0000000000..739422cbfa
--- /dev/null
+++ b/dom/animation/test/mozilla/empty.html
@@ -0,0 +1,2 @@
+<!DOCTYPE html>
+<script src="../testcommon.js"></script>
diff --git a/dom/animation/test/mozilla/file_deferred_start.html b/dom/animation/test/mozilla/file_deferred_start.html
new file mode 100644
index 0000000000..863fc80fec
--- /dev/null
+++ b/dom/animation/test/mozilla/file_deferred_start.html
@@ -0,0 +1,179 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="../testcommon.js"></script>
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<style>
+@keyframes empty { }
+.target {
+  /* Element needs geometry to be eligible for layerization */
+  width: 100px;
+  height: 100px;
+  background-color: white;
+}
+</style>
+<body>
+<script>
+'use strict';
+
+function waitForDocLoad() {
+  return new Promise((resolve, reject) => {
+    if (document.readyState === 'complete') {
+      resolve();
+    } else {
+      window.addEventListener('load', resolve);
+    }
+  });
+}
+
+function waitForPaints() {
+  return new Promise((resolve, reject) => {
+    waitForAllPaintsFlushed(resolve);
+  });
+}
+
+promise_test(async t => {
+  // Test that empty animations actually start.
+  //
+  // Normally we tie the start of animations to when their first frame of
+  // the animation is rendered. However, for animations that don't actually
+  // trigger a paint (e.g. because they are empty, or are animating something
+  // that doesn't render or is offscreen) we want to make sure they still
+  // start.
+  //
+  // Before we start, wait for the document to finish loading, then create
+  // div element, and wait for painting. This is because during loading we will
+  // have other paint events taking place which might, by luck, happen to
+  // trigger animations that otherwise would not have been triggered, leading to
+  // false positives.
+  //
+  // As a result, it's better to wait until we have a more stable state before
+  // continuing.
+  await waitForDocLoad();
+
+  const div = addDiv(t);
+
+  await waitForPaints();
+
+  div.style.animation = 'empty 1000s';
+  const animation = div.getAnimations()[0];
+
+  let promiseCallbackDone = false;
+  animation.ready.then(() => {
+    promiseCallbackDone = true;
+  }).catch(() => {
+    assert_unreached('ready promise was rejected');
+  });
+
+  // We need to wait for up to three frames. This is because in some
+  // cases it can take up to two frames for the initial layout
+  // to take place. Even after that happens we don't actually resolve the
+  // ready promise until the following tick.
+  await waitForAnimationFrames(3);
+
+  assert_true(promiseCallbackDone,
+              'ready promise for an empty animation was resolved'
+              + ' within three animation frames');
+}, 'Animation.ready is resolved for an empty animation');
+
+// Test that compositor animations with delays get synced correctly
+//
+// NOTE: It is important that we DON'T use
+// SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh here since that takes
+// us through a different code path.
+promise_test(async t => {
+  assert_false(SpecialPowers.DOMWindowUtils.isTestControllingRefreshes,
+               'Test should run without the refresh driver being under'
+               + ' test control');
+
+  // This test only applies to compositor animations
+  if (!isOMTAEnabled()) {
+    return;
+  }
+
+  const div = addDiv(t, { class: 'target' });
+
+  // As with the above test, any stray paints can cause this test to produce
+  // a false negative (that is, pass when it should fail). To avoid this we
+  // wait for paints and only then do we commence the test.
+  await waitForPaints();
+
+  const animation =
+    div.animate({ transform: [ 'translate(0px)', 'translate(100px)' ] },
+                { duration: 400 * MS_PER_SEC,
+                  delay: -200 * MS_PER_SEC });
+
+  await waitForAnimationReadyToRestyle(animation);
+
+  await waitForPaints();
+
+  const transformStr =
+    SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+  const translateX = getTranslateXFromTransform(transformStr);
+
+  // If the delay has been applied we should be about half-way through
+  // the animation. However, if we applied it twice we will be at the
+  // end of the animation already so check that we are roughly half way
+  // through.
+  assert_between_inclusive(translateX, 40, 75,
+      'Animation is about half-way through on the compositor');
+}, 'Starting an animation with a delay starts from the correct point');
+
+// Test that compositor animations with a playback rate start at the
+// appropriate point.
+//
+// NOTE: As with the previous test, it is important that we DON'T use
+// SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh here since that takes
+// us through a different code path.
+promise_test(async t => {
+  assert_false(SpecialPowers.DOMWindowUtils.isTestControllingRefreshes,
+               'Test should run without the refresh driver being under'
+               + ' test control');
+
+  // This test only applies to compositor animations
+  if (!isOMTAEnabled()) {
+    return;
+  }
+
+  const div = addDiv(t, { class: 'target' });
+
+  // Wait for the document to load and painting (see notes in previous test).
+  await waitForPaints();
+
+  const animation =
+    div.animate({ transform: [ 'translate(0px)', 'translate(100px)' ] },
+                200 * MS_PER_SEC);
+  animation.currentTime = 100 * MS_PER_SEC;
+  animation.playbackRate = 0.1;
+
+  await waitForPaints();
+
+  const transformStr =
+    SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+  const translateX = getTranslateXFromTransform(transformStr);
+
+  // We pass the playback rate to the compositor independently and we have
+  // tests to ensure that it is correctly applied there. However, if, when
+  // we resolve the start time of the pending animation, we fail to
+  // incorporate the playback rate, we will end up starting from the wrong
+  // point and the current time calculated on the compositor will be wrong.
+  assert_between_inclusive(translateX, 25, 75,
+      'Animation is about half-way through on the compositor');
+}, 'Starting an animation with a playbackRate starts from the correct point');
+
+function getTranslateXFromTransform(transformStr) {
+  const matrixComponents =
+    transformStr.startsWith('matrix(')
+    ? transformStr.substring('matrix('.length, transformStr.length-1)
+                  .split(',')
+                  .map(component => Number(component))
+    : [];
+  assert_equals(matrixComponents.length, 6,
+                'Got a valid transform matrix on the compositor'
+                + ' (got: "' + transformStr + '")');
+
+  return matrixComponents[4];
+}
+
+done();
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/file_disable_animations_api_autoremove.html b/dom/animation/test/mozilla/file_disable_animations_api_autoremove.html
new file mode 100644
index 0000000000..79cb508467
--- /dev/null
+++ b/dom/animation/test/mozilla/file_disable_animations_api_autoremove.html
@@ -0,0 +1,69 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="../testcommon.js"></script>
+<body>
+<script>
+'use strict';
+
+promise_test(async t => {
+  const div = addDiv(t);
+
+  const animA = div.animate({ opacity: 1 }, { duration: 1, fill: 'forwards' });
+  const animB = div.animate({ opacity: 1 }, { duration: 1, fill: 'forwards' });
+
+  // This should be assert_not_own_property but our local copy of testharness.js
+  // is old.
+  assert_equals(
+    animA.replaceState,
+    undefined,
+    'Should not have a replaceState member'
+  );
+
+  animA.addEventListener(
+    'remove',
+    t.step_func(() => {
+      assert_unreached('Should not fire a remove event');
+    })
+  );
+
+  // Allow a chance for the remove event to be fired
+
+  await animA.finished;
+  await waitForNextFrame();
+}, 'Remove events should not be fired if the pref is not set');
+
+promise_test(async t => {
+  const div = addDiv(t);
+  div.style.opacity = '0.1';
+
+  const animA = div.animate(
+    { opacity: 0.2 },
+    { duration: 1, fill: 'forwards' }
+  );
+  const animB = div.animate(
+    { opacity: 0.3, composite: 'add' },
+    { duration: 1, fill: 'forwards' }
+  );
+
+  await animA.finished;
+
+  assert_approx_equals(
+    parseFloat(getComputedStyle(div).opacity),
+    0.5,
+    0.0001,
+    'Covered animation should still contribute to effect stack when adding'
+  );
+
+  animB.cancel();
+
+  assert_approx_equals(
+    parseFloat(getComputedStyle(div).opacity),
+    0.2,
+    0.0001,
+    'Covered animation should still contribute to animated style when replacing'
+  );
+}, 'Covered animations should still affect style if the pref is not set');
+
+done();
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/file_disable_animations_api_compositing.html b/dom/animation/test/mozilla/file_disable_animations_api_compositing.html
new file mode 100644
index 0000000000..6d9ba35dc0
--- /dev/null
+++ b/dom/animation/test/mozilla/file_disable_animations_api_compositing.html
@@ -0,0 +1,137 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="../testcommon.js"></script>
+<body>
+<script>
+'use strict';
+
+test(t => {
+  const anim = addDiv(t).animate(
+    { marginLeft: ['0px', '10px'] },
+    {
+      duration: 100 * MS_PER_SEC,
+      iterations: 10,
+      iterationComposite: 'accumulate',
+      composite: 'add',
+    }
+  );
+  assert_false(
+    'iterationComposite' in anim.effect,
+    'The KeyframeEffect.iterationComposite member is not present'
+  );
+  assert_false(
+    'composite' in anim.effect,
+    'The KeyframeEffect.composite member is not present'
+  );
+}, 'The iterationComposite and composite members are not present on Animation'
+   + ' when the compositing pref is disabled');
+
+test(t => {
+  const div = addDiv(t);
+  const anim = div.animate(
+    { marginLeft: ['0px', '10px'] },
+    {
+      duration: 100 * MS_PER_SEC,
+      iterations: 10,
+      iterationComposite: 'accumulate',
+    }
+  );
+  anim.pause();
+  anim.currentTime = 200 * MS_PER_SEC;
+
+  assert_equals(
+    getComputedStyle(div).marginLeft,
+    '0px',
+    'Animated style should NOT accumulate'
+  );
+}, 'KeyframeEffectOptions.iterationComposite should be ignored if the'
+   + ' compositing pref is disabled');
+
+test(t => {
+  const div = addDiv(t);
+  const anim1 = div.animate(
+    { marginLeft: ['0px', '100px'] },
+    { duration: 100 * MS_PER_SEC }
+  );
+  anim1.pause();
+  anim1.currentTime = 50 * MS_PER_SEC;
+
+  const anim2 = div.animate(
+    { marginLeft: ['0px', '100px'] },
+    { duration: 100 * MS_PER_SEC, composite: 'add' }
+  );
+  anim2.pause();
+  anim2.currentTime = 50 * MS_PER_SEC;
+
+  assert_equals(
+    getComputedStyle(div).marginLeft,
+    '50px',
+    'Animations should NOT add together'
+  );
+}, 'KeyframeEffectOptions.composite should be ignored if the'
+   + ' compositing pref is disabled');
+
+test(t => {
+  const div = addDiv(t);
+  const anim1 = div.animate({ marginLeft: ['0px', '100px'] }, 100 * MS_PER_SEC);
+  anim1.pause();
+  anim1.currentTime = 50 * MS_PER_SEC;
+
+  const anim2 = div.animate(
+    [
+      { marginLeft: '0px', composite: 'add' },
+      { marginLeft: '100px', composite: 'add' },
+    ],
+    100 * MS_PER_SEC
+  );
+  anim2.pause();
+  anim2.currentTime = 50 * MS_PER_SEC;
+
+  assert_equals(
+    getComputedStyle(div).marginLeft,
+    '50px',
+    'Animations should NOT add together'
+  );
+}, 'composite member is ignored on keyframes when using array notation');
+
+test(t => {
+  const div = addDiv(t);
+  const anim1 = div.animate(
+    { marginLeft: ['0px', '100px'] },
+    100 * MS_PER_SEC
+  );
+  anim1.pause();
+  anim1.currentTime = 50 * MS_PER_SEC;
+
+  const anim2 = div.animate(
+    { marginLeft: ['0px', '100px'], composite: ['add', 'add'] },
+    100 * MS_PER_SEC
+  );
+  anim2.pause();
+  anim2.currentTime = 50 * MS_PER_SEC;
+
+  assert_equals(
+    getComputedStyle(div).marginLeft,
+    '50px',
+    'Animations should NOT add together'
+  );
+}, 'composite member is ignored on keyframes when using object notation');
+
+test(t => {
+  const anim = addDiv(t).animate(
+    { marginLeft: ['0px', '10px'] },
+    100 * MS_PER_SEC
+  );
+
+  for (let frame of anim.effect.getKeyframes()) {
+    assert_false(
+      'composite' in frame,
+      'The BaseComputedKeyframe.composite member is not present'
+    );
+  }
+}, 'composite member is hidden from the result of ' +
+   'KeyframeEffect::getKeyframes()');
+
+done();
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/file_disable_animations_api_get_animations.html b/dom/animation/test/mozilla/file_disable_animations_api_get_animations.html
new file mode 100644
index 0000000000..3d484444a7
--- /dev/null
+++ b/dom/animation/test/mozilla/file_disable_animations_api_get_animations.html
@@ -0,0 +1,20 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="../testcommon.js"></script>
+<body>
+<script>
+'use strict';
+
+test(t => {
+  assert_false('getAnimations' in addDiv(t));
+}, 'Element.getAnimations() is not available when getAnimations pref is'
+    + ' disabled');
+
+test(t => {
+  assert_false('getAnimations' in document);
+}, 'Document.getAnimations() is not available when getAnimations pref is'
+    + ' disabled');
+
+done();
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/file_disable_animations_api_implicit_keyframes.html b/dom/animation/test/mozilla/file_disable_animations_api_implicit_keyframes.html
new file mode 100644
index 0000000000..9cd05e7d40
--- /dev/null
+++ b/dom/animation/test/mozilla/file_disable_animations_api_implicit_keyframes.html
@@ -0,0 +1,48 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="../testcommon.js"></script>
+<body>
+<script>
+'use strict';
+
+// Tests for cases we should throw an exception for if implicit keyframes are
+// disabled.
+var gTests = [
+  { desc: "single Keyframe value",
+    keyframes: { left: "100px" } },
+  { desc: "single Keyframe with no offset",
+    keyframes: [{ left: "100px" }] },
+  { desc: "single Keyframe with 0% offset",
+    keyframes: [{ left: "100px", offset: 0 }] },
+  { desc: "single Keyframe with 100% offset",
+    keyframes: [{ left: "100px", offset: 1 }] },
+  { desc: "multiple Keyframes with missing 0% Keyframe",
+    keyframes: [{ left: "100px", offset: 0.25 },
+                { left: "200px", offset: 0.50 },
+                { left: "300px", offset: 1.00 }] },
+  { desc: "multiple Keyframes with missing 100% Keyframe",
+    keyframes: [{ left: "100px", offset: 0.00 },
+                { left: "200px", offset: 0.50 },
+                { left: "300px", offset: 0.75 }] },
+  { desc: "multiple Keyframes with missing properties on first Keyframe",
+    keyframes: [{ left: "100px", offset: 0.0 },
+                { left: "200px", top: "200px", offset: 0.5 },
+                { left: "300px", top: "300px", offset: 1.0 }] },
+  { desc: "multiple Keyframes with missing properties on last Keyframe",
+    keyframes: [{ left: "100px", top: "200px", offset: 0.0 },
+                { left: "200px", top: "200px", offset: 0.5 },
+                { left: "300px", offset: 1.0 }] },
+];
+
+gTests.forEach(function(subtest) {
+  test(function(t) {
+    var div = addDiv(t);
+    assert_throws("NotSupportedError", function() {
+      div.animate(subtest.keyframes, 100 * MS_PER_SEC);
+    });
+  }, "Element.animate() throws with " + subtest.desc);
+});
+
+done();
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/file_disable_animations_api_timelines.html b/dom/animation/test/mozilla/file_disable_animations_api_timelines.html
new file mode 100644
index 0000000000..39fedb299a
--- /dev/null
+++ b/dom/animation/test/mozilla/file_disable_animations_api_timelines.html
@@ -0,0 +1,30 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="../testcommon.js"></script>
+<body>
+<script>
+'use strict';
+
+test(t => {
+  assert_false(
+    window.hasOwnProperty('DocumentTimeline'),
+    'DocumentTimeline should not be exposed on the global'
+  );
+  assert_false(
+    window.hasOwnProperty('AnimationTimeline'),
+    'AnimationTimeline should not be exposed on the global'
+  );
+  assert_false(
+    'timeline' in document,
+    'document should not have a timeline property'
+  );
+
+  const anim = addDiv(t).animate(null);
+  assert_false(
+    'timeline' in anim,
+    'Animation should not have a timeline property'
+  );
+}, 'Timeline-related interfaces and members are disabled');
+
+done();
+</script>
diff --git a/dom/animation/test/mozilla/file_discrete_animations.html b/dom/animation/test/mozilla/file_discrete_animations.html
new file mode 100644
index 0000000000..e0de609bc5
--- /dev/null
+++ b/dom/animation/test/mozilla/file_discrete_animations.html
@@ -0,0 +1,122 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Test Mozilla-specific discrete animatable properties</title>
+<script type="application/javascript" src="../testcommon.js"></script>
+</head>
+<body>
+<script>
+"use strict";
+
+const gMozillaSpecificProperties = {
+  "-moz-box-align": {
+    // https://developer.mozilla.org/en/docs/Web/CSS/box-align
+    from: "center",
+    to: "stretch"
+  },
+  "-moz-box-direction": {
+    // https://developer.mozilla.org/en/docs/Web/CSS/box-direction
+    from: "reverse",
+    to: "normal"
+  },
+  "-moz-box-ordinal-group": {
+    // https://developer.mozilla.org/en/docs/Web/CSS/box-ordinal-group
+    from: "1",
+    to: "5"
+  },
+  "-moz-box-orient": {
+    // https://www.w3.org/TR/css-flexbox-1/
+    from: "horizontal",
+    to: "vertical"
+  },
+  "-moz-box-pack": {
+    // https://www.w3.org/TR/2009/WD-css3-flexbox-20090723/#propdef-box-pack
+    from: "center",
+    to: "end"
+  },
+  "-moz-float-edge": {
+    // https://developer.mozilla.org/en/docs/Web/CSS/-moz-float-edge
+    from: "margin-box",
+    to: "content-box"
+  },
+  "-moz-force-broken-image-icon": {
+    // https://developer.mozilla.org/en/docs/Web/CSS/-moz-force-broken-image-icon
+    from: "1",
+    to: "0"
+  },
+  "-moz-text-size-adjust": {
+    // https://drafts.csswg.org/css-size-adjust/#propdef-text-size-adjust
+    from: "none",
+    to: "auto"
+  },
+  "-webkit-text-stroke-width": {
+    // https://compat.spec.whatwg.org/#propdef--webkit-text-stroke-width
+    from: "10px",
+    to: "50px"
+  }
+}
+
+for (let property in gMozillaSpecificProperties) {
+  const testData = gMozillaSpecificProperties[property];
+  const from = testData.from;
+  const to = testData.to;
+  const idlName = propertyToIDL(property);
+  const keyframes = {};
+  keyframes[idlName] = [from, to];
+
+  test(t => {
+    const div = addDiv(t);
+    const animation = div.animate(keyframes,
+                                  { duration: 1000, fill: "both" });
+    testAnimationSamples(animation, idlName,
+                         [{ time: 0,    expected: from.toLowerCase() },
+                          { time: 499,  expected: from.toLowerCase() },
+                          { time: 500,  expected: to.toLowerCase() },
+                          { time: 1000, expected: to.toLowerCase() }]);
+  }, property + " should animate between '"
+   + from + "' and '" + to + "' with linear easing");
+
+  test(function(t) {
+    // Easing: http://cubic-bezier.com/#.68,0,1,.01
+    // With this curve, we don't reach the 50% point until about 95% of
+    // the time has expired.
+    const div = addDiv(t);
+    const animation = div.animate(keyframes,
+                                  { duration: 1000, fill: "both",
+                                    easing: "cubic-bezier(0.68,0,1,0.01)" });
+    testAnimationSamples(animation, idlName,
+                         [{ time: 0,    expected: from.toLowerCase() },
+                          { time: 940,  expected: from.toLowerCase() },
+                          { time: 960,  expected: to.toLowerCase() }]);
+  }, property + " should animate between '"
+   + from + "' and '" + to + "' with effect easing");
+
+  test(function(t) {
+    // Easing: http://cubic-bezier.com/#.68,0,1,.01
+    // With this curve, we don't reach the 50% point until about 95% of
+    // the time has expired.
+    keyframes.easing = "cubic-bezier(0.68,0,1,0.01)";
+    const div = addDiv(t);
+    const animation = div.animate(keyframes,
+                                  { duration: 1000, fill: "both" });
+    testAnimationSamples(animation, idlName,
+                         [{ time: 0,    expected: from.toLowerCase() },
+                          { time: 940,  expected: from.toLowerCase() },
+                          { time: 960,  expected: to.toLowerCase() }]);
+  }, property + " should animate between '"
+   + from + "' and '" + to + "' with keyframe easing");
+}
+
+function testAnimationSamples(animation, idlName, testSamples) {
+  const target = animation.effect.target;
+  testSamples.forEach(testSample => {
+    animation.currentTime = testSample.time;
+    assert_equals(getComputedStyle(target)[idlName], testSample.expected,
+                  "The value should be " + testSample.expected +
+                  " at " + testSample.time + "ms");
+  });
+}
+
+done();
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/file_restyles.html b/dom/animation/test/mozilla/file_restyles.html
new file mode 100644
index 0000000000..8d72cb6c44
--- /dev/null
+++ b/dom/animation/test/mozilla/file_restyles.html
@@ -0,0 +1,2275 @@
+<!doctype html>
+<head>
+<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
+<meta charset=utf-8>
+<title>Tests restyles caused by animations</title>
+<script>
+const ok = opener.ok.bind(opener);
+const is = opener.is.bind(opener);
+const todo = opener.todo.bind(opener);
+const todo_is = opener.todo_is.bind(opener);
+const info = opener.info.bind(opener);
+const original_finish = opener.SimpleTest.finish;
+const SimpleTest = opener.SimpleTest;
+const add_task = opener.add_task;
+SimpleTest.finish = function finish() {
+  self.close();
+  original_finish();
+}
+</script>
+<script src="/tests/SimpleTest/EventUtils.js"></script>
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<script src="../testcommon.js"></script>
+<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
+<style>
+@keyframes background-position {
+  0% {
+    background-position: -25px center;
+  }
+
+  40%,
+  100% {
+    background-position: 36px center;
+  }
+}
+@keyframes opacity {
+  from { opacity: 1; }
+  to { opacity: 0; }
+}
+@keyframes opacity-without-end-value {
+  from { opacity: 0; }
+}
+@keyframes on-main-thread {
+  from { z-index: 0; }
+  to { z-index: 999; }
+}
+@keyframes rotate {
+  from { transform: rotate(0deg); }
+  to { transform: rotate(360deg); }
+}
+@keyframes move-in {
+  from { transform: translate(120%, 120%); }
+  to { transform: translate(0%, 0%); }
+}
+@keyframes background-color {
+  from { background-color: rgb(255, 0, 0,); }
+  to { background-color: rgb(0, 255, 0,); }
+}
+div {
+  /* Element needs geometry to be eligible for layerization */
+  width: 100px;
+  height: 100px;
+  background-color: white;
+}
+progress:not(.stop)::-moz-progress-bar {
+  animation: on-main-thread 100s;
+}
+body {
+  /*
+   * set overflow:hidden to avoid accidentally unthrottling animations to update
+   * the overflow region.
+   */
+  overflow: hidden;
+}
+</style>
+</head>
+<body>
+<script>
+'use strict';
+
+// Returns observed animation restyle markers when |funcToMakeRestyleHappen|
+// is called.
+// NOTE: This function is synchronous version of the above observeStyling().
+// Unlike the above observeStyling, this function takes a callback function,
+// |funcToMakeRestyleHappen|, which may be expected to trigger a synchronous
+// restyles, and returns any restyle markers produced by calling that function.
+function observeAnimSyncStyling(funcToMakeRestyleHappen) {
+  const docShell = getDocShellForObservingRestylesForWindow(window);
+
+  funcToMakeRestyleHappen();
+
+  const markers = docShell.popProfileTimelineMarkers();
+  docShell.recordProfileTimelineMarkers = false;
+  return Array.prototype.filter.call(markers, (marker, index) => {
+    return marker.name == 'Styles' && marker.isAnimationOnly;
+  });
+}
+
+function ensureElementRemoval(aElement) {
+  return new Promise(resolve => {
+    aElement.remove();
+    waitForAllPaintsFlushed(resolve);
+  });
+}
+
+function waitForWheelEvent(aTarget) {
+  return new Promise(resolve => {
+    // Get the scrollable target element position in this window coordinate
+    // system to send a wheel event to the element.
+    const targetRect = aTarget.getBoundingClientRect();
+    const centerX = targetRect.left + targetRect.width / 2;
+    const centerY = targetRect.top + targetRect.height / 2;
+
+    sendWheelAndPaintNoFlush(aTarget, centerX, centerY,
+                             { deltaMode: WheelEvent.DOM_DELTA_PIXEL,
+                               deltaY: targetRect.height },
+                             resolve);
+  });
+}
+
+const omtaEnabled = isOMTAEnabled();
+
+function add_task_if_omta_enabled(test) {
+  if (!omtaEnabled) {
+    info(test.name + " is skipped because OMTA is disabled");
+    return;
+  }
+  add_task(test);
+}
+
+// We need to wait for all paints before running tests to avoid contaminations
+// from styling of this document itself.
+waitForAllPaints(() => {
+  add_task(async function () {
+    // Start vsync rate measurement in after a RAF callback.
+    await waitForNextFrame();
+
+    const timeAtStart = document.timeline.currentTime;
+    await waitForAnimationFrames(5);
+    const vsyncRate = (document.timeline.currentTime - timeAtStart) / 5;
+
+    // In this test we basically observe restyling counts in 5 frames, if it
+    // takes over 200ms during the 5 frames, this test will fail. So
+    // "200ms / 5 = 40ms" is a threshold whether the test works as expected or
+    // not. We'd take 5ms additional tolerance here.
+    // Note that the 200ms is a period we unthrottle throttled animations that
+    // at least one of the animating styles produces change hints causing
+    // overflow, the value is defined in
+    // KeyframeEffect::OverflowRegionRefreshInterval.
+    if (vsyncRate > 40 - 5) {
+      ok(true, `the vsync rate ${vsyncRate} on this machine is too slow to run this test`);
+      SimpleTest.finish();
+    }
+  });
+
+  add_task(async function restyling_for_main_thread_animations() {
+    const div = addDiv(null, { style: 'animation: on-main-thread 100s' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 5,
+       'CSS animations running on the main-thread should update style ' +
+       'on the main thread');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_for_main_thread_animations_progress_bar_pseudo() {
+    const progress = document.createElement("progress");
+    document.body.appendChild(progress);
+
+    await waitForNextFrame();
+    await waitForNextFrame();
+
+    let markers = await observeStyling(5);
+    is(markers.length, 5,
+       'CSS animations running on the main-thread should update style ' +
+       'on the main thread on ::-moz-progress-bar');
+    progress.classList.add("stop");
+    await waitForNextFrame();
+    await waitForNextFrame();
+
+    markers = await observeStyling(5);
+    is(markers.length, 0, 'Animation is correctly removed');
+    await ensureElementRemoval(progress);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_for_compositor_animations() {
+    const div = addDiv(null, { style: 'animation: opacity 100s' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'CSS animations running on the compositor should not update style ' +
+       'on the main thread');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_for_compositor_transitions() {
+    const div = addDiv(null, { style: 'transition: opacity 100s; opacity: 0' });
+    getComputedStyle(div).opacity;
+    div.style.opacity = 1;
+
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'CSS transitions running on the compositor should not update style ' +
+       'on the main thread');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_when_animation_duration_is_changed() {
+    const div = addDiv(null, { style: 'animation: opacity 100s' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    div.animationDuration = '200s';
+
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Animations running on the compositor should not update style ' +
+       'on the main thread');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function only_one_restyling_after_finish_is_called() {
+    const div = addDiv(null, { style: 'animation: opacity 100s' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    animation.finish();
+
+    let markers = await observeStyling(1);
+    is(markers.length, 1,
+       'Animations running on the compositor should only update style once ' +
+       'after finish() is called');
+
+    markers = await observeStyling(1);
+    todo_is(markers.length, 0,
+            'Bug 1415457: Animations running on the compositor should only ' +
+            'update style once after finish() is called');
+
+    markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Finished animations should never update style after one ' +
+       'restyle happened for finish()');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_restyling_mouse_movement_on_finished_transition() {
+    const div = addDiv(null, { style: 'transition: opacity 1ms; opacity: 0' });
+    getComputedStyle(div).opacity;
+    div.style.opacity = 1;
+
+    const animation = div.getAnimations()[0];
+    const initialRect = div.getBoundingClientRect();
+
+    await animation.finished;
+    let markers = await observeStyling(1);
+    is(markers.length, 1,
+       'Finished transitions should restyle once after Animation.finished ' +
+       'was fulfilled');
+
+    let mouseX = initialRect.left + initialRect.width / 2;
+    let mouseY = initialRect.top + initialRect.height / 2;
+    markers = await observeStyling(5, () => {
+      // We can't use synthesizeMouse here since synthesizeMouse causes
+      // layout flush.
+      synthesizeMouseAtPoint(mouseX++, mouseY++,
+                             { type: 'mousemove' }, window);
+    });
+
+    is(markers.length, 0,
+       'Finished transitions should never cause restyles when mouse is moved ' +
+       'on the transitions');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_restyling_mouse_movement_on_finished_animation() {
+    const div = addDiv(null, { style: 'animation: opacity 1ms' });
+    const animation = div.getAnimations()[0];
+
+    const initialRect = div.getBoundingClientRect();
+
+    await animation.finished;
+    let markers = await observeStyling(1);
+    is(markers.length, 1,
+       'Finished animations should restyle once after Animation.finished ' +
+       'was fulfilled');
+
+    let mouseX = initialRect.left + initialRect.width / 2;
+    let mouseY = initialRect.top + initialRect.height / 2;
+    markers = await observeStyling(5, () => {
+      // We can't use synthesizeMouse here since synthesizeMouse causes
+      // layout flush.
+      synthesizeMouseAtPoint(mouseX++, mouseY++,
+                             { type: 'mousemove' }, window);
+    });
+
+    is(markers.length, 0,
+       'Finished animations should never cause restyles when mouse is moved ' +
+       'on the animations');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_compositor_animations_out_of_view_element() {
+    const div = addDiv(null,
+      { style: 'animation: opacity 100s; transform: translateY(-400px);' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the compositor in an out-of-view element ' +
+       'should never cause restyles');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_restyling_main_thread_animations_out_of_view_element() {
+    const div = addDiv(null,
+      { style: 'animation: on-main-thread 100s; transform: translateY(-400px);' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the main-thread in an out-of-view element ' +
+       'should never cause restyles');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_compositor_animations_in_scrolled_out_element() {
+    const parentElement = addDiv(null,
+      { style: 'overflow-y: scroll; height: 20px;' });
+    const div = addDiv(null,
+      { style: 'animation: opacity 100s; position: relative; top: 100px;' });
+    parentElement.appendChild(div);
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the compositor for elements ' +
+       'which are scrolled out should never cause restyles');
+
+    await ensureElementRemoval(parentElement);
+  });
+
+  add_task(
+    async function no_restyling_missing_keyframe_opacity_animations_on_scrolled_out_element() {
+      const parentElement = addDiv(null,
+        { style: 'overflow-y: scroll; height: 20px;' });
+      const div = addDiv(null,
+        { style: 'animation: opacity-without-end-value 100s; ' +
+                 'position: relative; top: 100px;' });
+      parentElement.appendChild(div);
+      const animation = div.getAnimations()[0];
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+
+      is(markers.length, 0,
+         'Opacity animations on scrolled out elements should never cause ' +
+         'restyles even if the animation has missing keyframes');
+
+      await ensureElementRemoval(parentElement);
+    }
+  );
+
+  add_task(
+    async function restyling_transform_animations_in_scrolled_out_element() {
+      // Make sure we start from the state right after requestAnimationFrame.
+      await waitForFrame();
+
+      const parentElement = addDiv(null,
+        { style: 'overflow-y: scroll; height: 20px;' });
+      const div = addDiv(null,
+        { style: 'animation: rotate 100s infinite; position: relative; top: 100px;' });
+      parentElement.appendChild(div);
+      const animation = div.getAnimations()[0];
+      let timeAtStart = document.timeline.currentTime;
+
+      ok(!animation.isRunningOnCompositor,
+         'The transform animation is not running on the compositor');
+
+      let markers;
+      let now;
+      let elapsed;
+      while (true) {
+        now = document.timeline.currentTime;
+        elapsed = (now - timeAtStart);
+        markers = await observeStyling(1);
+        if (markers.length) {
+          break;
+        }
+      }
+      // If the current time has elapsed over 200ms since the animation was
+      // created, it means that the animation should have already
+      // unthrottled in this tick, let's see what we observe in this tick's
+      // restyling process.
+      // We use toPrecision here and below so 199.99999999999977 will turn into 200.
+      ok(elapsed.toPrecision(10) >= 200,
+           'Transform animation running on the element which is scrolled out ' +
+           'should be throttled until 200ms is elapsed. now: ' +
+            now + ' start time: ' + timeAtStart + ' elapsed:' + elapsed);
+
+      timeAtStart = document.timeline.currentTime;
+      markers = await observeStyling(1);
+      now = document.timeline.currentTime;
+      elapsed = (now - timeAtStart);
+
+      let expectedMarkersLengthValid;
+      // On the fence of 200 ms, we probably have 1 marker; but if we hit a bad rounding
+      // we might still have 0. But if it's > 200, we should have 1; and less we should have 0.
+      if (elapsed.toPrecision(10) == 200)
+        expectedMarkersLengthValid = markers.length < 2;
+      else if (elapsed.toPrecision(10) > 200)
+        expectedMarkersLengthValid = markers.length == 1;
+      else
+        expectedMarkersLengthValid = !markers.length;
+      ok(expectedMarkersLengthValid,
+         'Transform animation running on the element which is scrolled out ' +
+         'should be unthrottled after around 200ms have elapsed. now: ' +
+         now + ' start time: ' + timeAtStart + ' elapsed: ' + elapsed);
+
+      await ensureElementRemoval(parentElement);
+    }
+  );
+
+  add_task(
+    async function restyling_out_of_view_transform_animations_in_another_element() {
+      // Make sure we start from the state right after requestAnimationFrame.
+      await waitForFrame();
+
+      const parentElement = addDiv(null,
+        { style: 'overflow: hidden;' });
+      const div = addDiv(null,
+        { style: 'animation: move-in 100s infinite;' });
+      parentElement.appendChild(div);
+      const animation = div.getAnimations()[0];
+      let timeAtStart = document.timeline.currentTime;
+
+      ok(!animation.isRunningOnCompositor,
+         'The transform animation on out of view element ' +
+         'is not running on the compositor');
+
+      // Structure copied from restyling_transform_animations_in_scrolled_out_element
+      let markers;
+      let now;
+      let elapsed;
+      while (true) {
+        now = document.timeline.currentTime;
+        elapsed = (now - timeAtStart);
+        markers = await observeStyling(1);
+        if (markers.length) {
+          break;
+        }
+      }
+
+      ok(elapsed.toPrecision(10) >= 200,
+         'Transform animation running on out of view element ' +
+         'should be throttled until 200ms is elapsed. now: ' +
+            now + ' start time: ' + timeAtStart + ' elapsed:' + elapsed);
+
+      timeAtStart = document.timeline.currentTime;
+      markers = await observeStyling(1);
+      now = document.timeline.currentTime;
+      elapsed = (now - timeAtStart);
+
+      let expectedMarkersLengthValid;
+      // On the fence of 200 ms, we probably have 1 marker; but if we hit a bad rounding
+      // we might still have 0. But if it's > 200, we should have 1; and less we should have 0.
+      if (elapsed.toPrecision(10) == 200)
+        expectedMarkersLengthValid = markers.length < 2;
+      else if (elapsed.toPrecision(10) > 200)
+        expectedMarkersLengthValid = markers.length == 1;
+      else
+        expectedMarkersLengthValid = !markers.length;
+      ok(expectedMarkersLengthValid,
+         'Transform animation running on out of view element ' +
+         'should be unthrottled after around 200ms have elapsed. now: ' +
+         now + ' start time: ' + timeAtStart +  ' elapsed: ' + elapsed);
+
+      await ensureElementRemoval(parentElement);
+    }
+  );
+
+  add_task(async function finite_transform_animations_in_out_of_view_element() {
+    const parentElement = addDiv(null, { style: 'overflow: hidden;' });
+    const div = addDiv(null);
+    const animation =
+      div.animate({ transform: [ 'translateX(120%)', 'translateX(100%)' ] },
+                                // This animation will move a bit but
+                                // will remain out-of-view.
+                  100 * MS_PER_SEC);
+    parentElement.appendChild(div);
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor, "Should not be running in compositor");
+
+    const markers = await observeStyling(20);
+    is(markers.length, 20,
+       'Finite transform animation in out-of-view element should never be ' +
+       'throttled');
+
+    await ensureElementRemoval(parentElement);
+  });
+
+  add_task(async function restyling_main_thread_animations_in_scrolled_out_element() {
+    const parentElement = addDiv(null,
+      { style: 'overflow-y: scroll; height: 20px;' });
+    const div = addDiv(null,
+      { style: 'animation: on-main-thread 100s; position: relative; top: 20px;' });
+    parentElement.appendChild(div);
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    let markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the main-thread for elements ' +
+       'which are scrolled out should never cause restyles');
+
+    await waitForWheelEvent(parentElement);
+
+    // Make sure we are ready to restyle before counting restyles.
+    await waitForFrame();
+
+    markers = await observeStyling(5);
+    is(markers.length, 5,
+       'Animations running on the main-thread which were in scrolled out ' +
+       'elements should update restyling soon after the element moved in ' +
+       'view by scrolling');
+
+    await ensureElementRemoval(parentElement);
+  });
+
+  add_task(async function restyling_main_thread_animations_in_nested_scrolled_out_element() {
+    const grandParent = addDiv(null,
+      { style: 'overflow-y: scroll; height: 20px;' });
+    const parentElement = addDiv(null,
+      { style: 'overflow-y: scroll; height: 100px;' });
+    const div = addDiv(null,
+      { style: 'animation: on-main-thread 100s; ' +
+               'position: relative; ' +
+               'top: 20px;' }); // This element is in-view in the parent, but
+                                // out of view in the grandparent.
+    grandParent.appendChild(parentElement);
+    parentElement.appendChild(div);
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    let markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the main-thread which are in nested elements ' +
+       'which are scrolled out should never cause restyles');
+
+    await waitForWheelEvent(grandParent);
+
+    await waitForFrame();
+
+    markers = await observeStyling(5);
+    is(markers.length, 5,
+       'Animations running on the main-thread which were in nested scrolled ' +
+       'out elements should update restyle soon after the element moved ' +
+       'in view by scrolling');
+
+    await ensureElementRemoval(grandParent);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_compositor_animations_in_visibility_hidden_element() {
+    const div = addDiv(null,
+     { style: 'animation: opacity 100s; visibility: hidden' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the compositor in visibility hidden element ' +
+       'should never cause restyles');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_main_thread_animations_move_out_of_view_by_scrolling() {
+    const parentElement = addDiv(null,
+      { style: 'overflow-y: scroll; height: 200px;' });
+    const div = addDiv(null,
+      { style: 'animation: on-main-thread 100s;' });
+    const pad = addDiv(null,
+      { style: 'height: 400px;' });
+    parentElement.appendChild(div);
+    parentElement.appendChild(pad);
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    await waitForWheelEvent(parentElement);
+
+    await waitForFrame();
+
+    const markers = await observeStyling(5);
+
+    // FIXME: We should reduce a redundant restyle here.
+    ok(markers.length >= 0,
+       'Animations running on the main-thread which are in scrolled out ' +
+       'elements should throttle restyling');
+
+    await ensureElementRemoval(parentElement);
+  });
+
+  add_task(async function restyling_main_thread_animations_moved_in_view_by_resizing() {
+    const parentElement = addDiv(null,
+      { style: 'overflow-y: scroll; height: 20px;' });
+    const div = addDiv(null,
+      { style: 'animation: on-main-thread 100s; position: relative; top: 100px;' });
+    parentElement.appendChild(div);
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    let markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Animations running on the main-thread which is in scrolled out ' +
+       'elements should not update restyling');
+
+    parentElement.style.height = '100px';
+    markers = await observeStyling(1);
+
+    is(markers.length, 1,
+       'Animations running on the main-thread which was in scrolled out ' +
+       'elements should update restyling soon after the element moved in ' +
+       'view by resizing');
+
+    await ensureElementRemoval(parentElement);
+  });
+
+  add_task(
+    async function restyling_animations_on_visibility_changed_element_having_child() {
+      const div = addDiv(null,
+       { style: 'animation: on-main-thread 100s;' });
+      const childElement = addDiv(null);
+      div.appendChild(childElement);
+
+      const animation = div.getAnimations()[0];
+
+      await waitForAnimationReadyToRestyle(animation);
+
+      // We don't check the animation causes restyles here since we already
+      // check it in the first test case.
+
+      div.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      const markers = await observeStyling(5);
+      todo_is(markers.length, 0,
+              'Animations running on visibility hidden element which ' +
+              'has a child whose visiblity is inherited from the element and ' +
+              'the element was initially visible');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(
+    async function restyling_animations_on_visibility_hidden_element_which_gets_visible() {
+      const div = addDiv(null,
+       { style: 'animation: on-main-thread 100s; visibility: hidden' });
+      const animation = div.getAnimations()[0];
+
+
+      await waitForAnimationReadyToRestyle(animation);
+      let markers = await observeStyling(5);
+
+      is(markers.length, 0,
+         'Animations running on visibility hidden element should never ' +
+         'cause restyles');
+
+      div.style.visibility = 'visible';
+      await waitForNextFrame();
+
+       markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running that was on visibility hidden element which ' +
+         'gets visible should not throttle restyling any more');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(async function restyling_animations_in_visibility_changed_parent() {
+    const parentDiv = addDiv(null, { style: 'visibility: hidden' });
+    const div = addDiv(null, { style: 'animation: on-main-thread 100s;' });
+    parentDiv.appendChild(div);
+
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    let markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running in visibility hidden parent should never cause ' +
+       'restyles');
+
+    parentDiv.style.visibility = 'visible';
+    await waitForNextFrame();
+
+    markers = await observeStyling(5);
+    is(markers.length, 5,
+       'Animations that was in visibility hidden parent should not ' +
+       'throttle restyling any more');
+
+    parentDiv.style.visibility = 'hidden';
+    await waitForNextFrame();
+
+    markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Animations that the parent element became visible should throttle ' +
+       'restyling again');
+
+    await ensureElementRemoval(parentDiv);
+  });
+
+  add_task(
+    async function restyling_animations_on_visibility_hidden_element_with_visibility_changed_children() {
+      const div = addDiv(null,
+       { style: 'animation: on-main-thread 100s; visibility: hidden' });
+      const animation = div.getAnimations()[0];
+
+      await waitForAnimationReadyToRestyle(animation);
+      let markers = await observeStyling(5);
+
+      is(markers.length, 0,
+         'Animations on visibility hidden element having no visible children ' +
+         'should never cause restyles');
+
+      const childElement = addDiv(null, { style: 'visibility: visible' });
+      div.appendChild(childElement);
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running on visibility hidden element but the element has ' +
+         'a visible child should not throttle restyling');
+
+      childElement.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      todo_is(markers.length, 0,
+              'Animations running on visibility hidden element that a child ' +
+              'has become invisible should throttle restyling');
+
+      childElement.style.visibility = 'visible';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running on visibility hidden element should not throttle ' +
+         'restyling after the invisible element changed to visible');
+
+      childElement.remove();
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      todo_is(markers.length, 0,
+              'Animations running on visibility hidden element should throttle ' +
+              'restyling again after all visible descendants were removed');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(
+    async function restyling_animations_on_visiblity_hidden_element_having_oof_child() {
+      const div = addDiv(null,
+        { style: 'animation: on-main-thread 100s; position: absolute' });
+      const childElement = addDiv(null,
+        { style: 'float: left; visibility: hidden' });
+      div.appendChild(childElement);
+
+      const animation = div.getAnimations()[0];
+
+      await waitForAnimationReadyToRestyle(animation);
+
+      // We don't check the animation causes restyles here since we already
+      // check it in the first test case.
+
+      div.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      const markers = await observeStyling(5);
+      is(markers.length, 0,
+         'Animations running on visibility hidden element which has an ' +
+         'out-of-flow child should throttle restyling');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(
+    async function restyling_animations_on_visibility_hidden_element_having_grandchild() {
+      // element tree:
+      //
+      //        root(visibility:hidden)
+      //       /                       \
+      //    childA                   childB
+      //    /     \                 /      \
+      //  AA       AB             BA        BB
+
+      const div = addDiv(null,
+       { style: 'animation: on-main-thread 100s; visibility: hidden' });
+
+      const childA = addDiv(null);
+      div.appendChild(childA);
+      const childB = addDiv(null);
+      div.appendChild(childB);
+
+      const grandchildAA = addDiv(null);
+      childA.appendChild(grandchildAA);
+      const grandchildAB = addDiv(null);
+      childA.appendChild(grandchildAB);
+
+      const grandchildBA = addDiv(null);
+      childB.appendChild(grandchildBA);
+      const grandchildBB = addDiv(null);
+      childB.appendChild(grandchildBB);
+
+      const animation = div.getAnimations()[0];
+
+      await waitForAnimationReadyToRestyle(animation);
+      let markers = await observeStyling(5);
+      is(markers.length, 0,
+         'Animations on visibility hidden element having no visible ' +
+         'descendants should never cause restyles');
+
+      childA.style.visibility = 'visible';
+      grandchildAA.style.visibility = 'visible';
+      grandchildAB.style.visibility = 'visible';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running on visibility hidden element but the element has ' +
+         'visible children should not throttle restyling');
+
+      // Make childA hidden again but both of grandchildAA and grandchildAB are
+      // still visible.
+      childA.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running on visibility hidden element that a child has ' +
+         'become invisible again but there are still visible children should ' +
+         'not throttle restyling');
+
+      // Make grandchildAA hidden but grandchildAB is still visible.
+      grandchildAA.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running on visibility hidden element that a grandchild ' +
+         'become invisible again but another grandchild is still visible ' +
+         'should not throttle restyling');
+
+
+      // Make childB and grandchildBA visible.
+      childB.style.visibility = 'visible';
+      grandchildBA.style.visibility = 'visible';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running on visibility hidden element but the element has ' +
+         'visible descendants should not throttle restyling');
+
+      // Make childB hidden but grandchildAB and grandchildBA are still visible.
+      childB.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running on visibility hidden element but the element has ' +
+         'visible grandchildren should not throttle restyling');
+
+      // Make grandchildAB hidden but grandchildBA is still visible.
+      grandchildAB.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations running on visibility hidden element but the element has ' +
+         'a visible grandchild should not throttle restyling');
+
+      // Make grandchildBA hidden. Now all descedants are invisible.
+      grandchildBA.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      todo_is(markers.length, 0,
+              'Animations on visibility hidden element that all descendants have ' +
+              'become invisible again should never cause restyles');
+
+      // Make childB visible.
+      childB.style.visibility = 'visible';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animations on visibility hidden element that has a visible child ' +
+         'should never cause restyles');
+
+      // Make childB invisible again
+      childB.style.visibility = 'hidden';
+      await waitForNextFrame();
+
+      markers = await observeStyling(5);
+      todo_is(markers.length, 0,
+              'Animations on visibility hidden element that the visible child ' +
+              'has become invisible again should never cause restyles');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task_if_omta_enabled(async function no_restyling_compositor_animations_after_pause_is_called() {
+    const div = addDiv(null, { style: 'animation: opacity 100s' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    animation.pause();
+
+    await animation.ready;
+
+    let markers = await observeStyling(1);
+    is(markers.length, 1,
+       'Animations running on the compositor should restyle once after ' +
+       'Animation.pause() was called');
+
+    markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Paused animations running on the compositor should never cause ' +
+       'restyles');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_restyling_main_thread_animations_after_pause_is_called() {
+    const div = addDiv(null, { style: 'animation: on-main-thread 100s' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    animation.pause();
+
+    await animation.ready;
+
+    let markers = await observeStyling(1);
+    is(markers.length, 1,
+       'Animations running on the main-thread should restyle once after ' +
+       'Animation.pause() was called');
+
+    markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Paused animations running on the main-thread should never cause ' +
+       'restyles');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function only_one_restyling_when_current_time_is_set_to_middle_of_duration() {
+    const div = addDiv(null, { style: 'animation: opacity 100s' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    animation.currentTime = 50 * MS_PER_SEC;
+
+    const markers = await observeStyling(5);
+    is(markers.length, 1,
+       'Bug 1235478: Animations running on the compositor should only once ' +
+       'update style when currentTime is set to middle of duration time');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function change_duration_and_currenttime() {
+    const div = addDiv(null);
+    const animation = div.animate({ opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    // Set currentTime to a time longer than duration.
+    animation.currentTime = 500 * MS_PER_SEC;
+
+    // Now the animation immediately get back from compositor.
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    // Extend the duration.
+    animation.effect.updateTiming({ duration: 800 * MS_PER_SEC });
+    const markers = await observeStyling(5);
+    is(markers.length, 1,
+       'Animations running on the compositor should update style ' +
+       'when duration is made longer than the current time');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function script_animation_on_display_none_element() {
+    const div = addDiv(null);
+    const animation = div.animate({ zIndex: [ '0', '999' ] },
+                                100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    div.style.display = 'none';
+
+    // We need to wait a frame to apply display:none style.
+    await waitForNextFrame();
+
+    is(animation.playState, 'running',
+       'Script animations keep running even when the target element has ' +
+       '"display: none" style');
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor,
+       'Script animations on "display:none" element should not run on the ' +
+       'compositor');
+
+    let markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Script animations on "display: none" element should not update styles');
+
+    div.style.display = '';
+
+    markers = await observeStyling(5);
+    is(markers.length, 5,
+       'Script animations restored from "display: none" state should update ' +
+       'styles');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function compositable_script_animation_on_display_none_element() {
+    const div = addDiv(null);
+    const animation = div.animate({ opacity: [ 0, 1 ] }, 100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    div.style.display = 'none';
+
+    // We need to wait a frame to apply display:none style.
+    await waitForNextFrame();
+
+    is(animation.playState, 'running',
+       'Opacity script animations keep running even when the target element ' +
+       'has "display: none" style');
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor,
+       'Opacity script animations on "display:none" element should not ' +
+       'run on the compositor');
+
+    let markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Opacity script animations on "display: none" element should not ' +
+       'update styles');
+
+    div.style.display = '';
+
+     markers = await observeStyling(1);
+    is(markers.length, 1,
+       'Script animations restored from "display: none" state should update ' +
+       'styles soon');
+
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor,
+       'Opacity script animations restored from "display: none" should be ' +
+       'run on the compositor in the next frame');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_for_empty_keyframes() {
+    const div = addDiv(null);
+    const animation = div.animate({ }, 100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(animation);
+    let markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations with no keyframes should not cause restyles');
+
+    animation.effect.setKeyframes({ zIndex: ['0', '999'] });
+    markers = await observeStyling(5);
+
+    is(markers.length, 5,
+       'Setting valid keyframes should cause regular animation restyles to ' +
+       'occur');
+
+    animation.effect.setKeyframes({ });
+    markers = await observeStyling(5);
+
+    is(markers.length, 1,
+       'Setting an empty set of keyframes should trigger a single restyle ' +
+       'to remove the previous animated style');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_when_animation_style_when_re_setting_same_animation_property() {
+    const div = addDiv(null, { style: 'animation: opacity 100s' });
+    const animation = div.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+    // Apply the same animation style
+    div.style.animation = 'opacity 100s';
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Applying same animation style '  +
+       'should never cause restyles');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function necessary_update_should_be_invoked() {
+    const div = addDiv(null, { style: 'animation: on-main-thread 100s' });
+    const animation = div.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+    await waitForAnimationFrames(5);
+    // Apply another animation style
+    div.style.animation = 'on-main-thread 110s';
+    const markers = await observeStyling(1);
+    // There should be two restyles.
+    // 1) Animation-only restyle for before applying the new animation style
+    // 2) Animation-only restyle for after applying the new animation style
+    is(markers.length, 2,
+       'Applying animation style with different duration '  +
+       'should restyle twice');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(
+    async function changing_cascading_result_for_main_thread_animation() {
+      const div = addDiv(null, { style: 'on-main-thread: blue' });
+      const animation = div.animate({ opacity: [0, 1],
+                                    zIndex: ['0', '999'] },
+                                  100 * MS_PER_SEC);
+      await waitForAnimationReadyToRestyle(animation);
+      ok(SpecialPowers.wrap(animation).isRunningOnCompositor,
+         'The opacity animation is running on the compositor');
+      // Make the z-index style as !important to cause an update
+      // to the cascade.
+      // Bug 1300982: The z-index animation should be no longer
+      // running on the main thread.
+      div.style.setProperty('z-index', '0', 'important');
+      const markers = await observeStyling(5);
+      todo_is(markers.length, 0,
+         'Changing cascading result for the property running on the main ' +
+         'thread does not cause synchronization layer of opacity animation ' +
+         'running on the compositor');
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task_if_omta_enabled(
+    async function animation_visibility_and_opacity() {
+      const div = addDiv(null);
+      const animation1 = div.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+      const animation2 = div.animate({ visibility: ['hidden', 'visible'] }, 100 * MS_PER_SEC);
+      await waitForAnimationReadyToRestyle(animation1);
+      await waitForAnimationReadyToRestyle(animation2);
+      const markers = await observeStyling(5);
+      is(markers.length, 5, 'The animation should not be throttled');
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(async function restyling_for_animation_on_orphaned_element() {
+    const div = addDiv(null);
+    const animation = div.animate({ marginLeft: [ '0px', '100px' ] },
+                                100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    div.remove();
+
+    let markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Animation on orphaned element should not cause restyles');
+
+    document.body.appendChild(div);
+
+    await waitForNextFrame();
+    markers = await observeStyling(5);
+
+    is(markers.length, 5,
+       'Animation on re-attached to the document begins to update style, got ' + markers.length);
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(
+    // Tests that if we remove an element from the document whose animation
+    // cascade needs recalculating, that it is correctly updated when it is
+    // re-attached to the document.
+    async function restyling_for_opacity_animation_on_re_attached_element() {
+      const div = addDiv(null, { style: 'opacity: 1 ! important' });
+      const animation = div.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+
+      await waitForAnimationReadyToRestyle(animation);
+      ok(!SpecialPowers.wrap(animation).isRunningOnCompositor,
+         'The opacity animation overridden by an !important rule is NOT ' +
+         'running on the compositor');
+
+      // Drop the !important rule to update the cascade.
+      div.style.setProperty('opacity', '1', '');
+
+      div.remove();
+
+      const markers = await observeStyling(5);
+      is(markers.length, 0,
+         'Opacity animation on orphaned element should not cause restyles');
+
+      document.body.appendChild(div);
+
+      // Need a frame to give the animation a chance to be sent to the
+      // compositor.
+      await waitForNextFrame();
+
+      ok(SpecialPowers.wrap(animation).isRunningOnCompositor,
+         'The opacity animation which is no longer overridden by the ' +
+         '!important rule begins running on the compositor even if the ' +
+         '!important rule had been dropped before the target element was ' +
+         'removed');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(
+    async function no_throttling_additive_animations_out_of_view_element() {
+      const div = addDiv(null, { style: 'transform: translateY(-400px);' });
+      const animation =
+        div.animate([{ visibility: 'visible' }],
+                    { duration: 100 * MS_PER_SEC, composite: 'add' });
+
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+
+      is(markers.length, 5,
+         'Additive animation has no keyframe whose offset is 0 or 1 in an ' +
+         'out-of-view element should not be throttled');
+      await ensureElementRemoval(div);
+    }
+  );
+
+  // Tests that missing keyframes animations don't throttle at all.
+  add_task(async function no_throttling_animations_out_of_view_element() {
+    const div = addDiv(null, { style: 'transform: translateY(-400px);' });
+    const animation =
+      div.animate([{ visibility: 'visible' }], 100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 5,
+       'Discrete animation has has no keyframe whose offset is 0 or 1 in an ' +
+       'out-of-view element should not be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  // Tests that missing keyframes animation on scrolled out element that the
+  // animation is not able to be throttled.
+  add_task(
+    async function no_throttling_missing_keyframe_animations_out_of_view_element() {
+      const div =
+        addDiv(null, { style: 'transform: translateY(-400px);' +
+                              'visibility: collapse;' });
+      const animation =
+        div.animate([{ visibility: 'visible' }], 100 * MS_PER_SEC);
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+      is(markers.length, 5,
+         'visibility animation has no keyframe whose offset is 0 or 1 in an ' +
+         'out-of-view element and produces change hint other than paint-only ' +
+         'change hint should not be throttled');
+      await ensureElementRemoval(div);
+    }
+  );
+
+  // Counter part of the above test.
+  add_task(async function no_restyling_discrete_animations_out_of_view_element() {
+    const div = addDiv(null, { style: 'transform: translateY(-400px);' });
+    const animation =
+      div.animate({ visibility: ['visible', 'hidden'] }, 100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Discrete animation running on the main-thread in an out-of-view ' +
+       'element should never cause restyles');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_restyling_while_computed_timing_is_not_changed() {
+    const div = addDiv(null);
+    const animation = div.animate({ zIndex: [ '0', '999' ] },
+                                  { duration: 100 * MS_PER_SEC,
+                                    easing: 'step-end' });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    // We possibly expect one restyle from the initial animation compose, in
+    // order to update animations, but nothing else.
+    ok(markers.length <= 1,
+       'Animation running on the main-thread while computed timing is not ' +
+       'changed should not cause extra restyles, got ' + markers.length);
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_throttling_animations_in_view_svg() {
+    const div = addDiv(null, { style: 'overflow: scroll;' +
+                                    'height: 100px; width: 100px;' });
+    const svg = addSVGElement(div, 'svg', { viewBox: '-10 -10 0.1 0.1',
+                                          width:   '50px',
+                                          height:  '50px' });
+    const rect = addSVGElement(svg, 'rect', { x:      '-10',
+                                            y:      '-10',
+                                            width:  '10',
+                                            height: '10',
+                                            fill:   'red' });
+    const animation = rect.animate({ fill: ['blue', 'lime'] }, 100 * MS_PER_SEC);
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 5,
+       'CSS animations on an in-view svg element with post-transform should ' +
+       'not be throttled.');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_throttling_animations_in_transformed_parent() {
+    const div = addDiv(null, { style: 'overflow: scroll;' +
+                                    'transform: translateX(50px);' });
+    const svg = addSVGElement(div, 'svg', { viewBox: '0 0 1250 1250',
+                                          width:   '40px',
+                                          height:  '40px' });
+    const rect = addSVGElement(svg, 'rect', { x:      '0',
+                                            y:      '0',
+                                            width:  '1250',
+                                            height: '1250',
+                                            fill:   'red' });
+    const animation = rect.animate({ fill: ['blue', 'lime'] }, 100 * MS_PER_SEC);
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 5,
+       'CSS animations on an in-view svg element which is inside transformed ' +
+       'parent should not be throttled.');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function throttling_animations_out_of_view_svg() {
+    const div = addDiv(null, { style: 'overflow: scroll;' +
+                                    'height: 100px; width: 100px;' });
+    const svg = addSVGElement(div, 'svg', { viewBox: '-10 -10 0.1 0.1',
+                                          width: '50px',
+                                          height: '50px' });
+    const rect = addSVGElement(svg, 'rect', { width: '10',
+                                            height: '10',
+                                            fill: 'red' });
+
+    const animation = rect.animate({ fill: ['blue', 'lime'] }, 100 * MS_PER_SEC);
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'CSS animations on an out-of-view svg element with post-transform ' +
+       'should be throttled.');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_throttling_animations_in_view_css_transform() {
+    const scrollDiv = addDiv(null, { style: 'overflow: scroll; ' +
+                                          'height: 100px; width: 100px;' });
+    const targetDiv = addDiv(null,
+                           { style: 'animation: on-main-thread 100s;' +
+                                    'transform: translate(-50px, -50px);' });
+    scrollDiv.appendChild(targetDiv);
+
+    const animation = targetDiv.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 5,
+       'CSS animation on an in-view element with pre-transform should not ' +
+       'be throttled.');
+
+    await ensureElementRemoval(scrollDiv);
+  });
+
+  add_task(async function throttling_animations_out_of_view_css_transform() {
+    const scrollDiv = addDiv(null, { style: 'overflow: scroll;' +
+                                          'height: 100px; width: 100px;' });
+    const targetDiv = addDiv(null,
+                           { style: 'animation: on-main-thread 100s;' +
+                                    'transform: translate(100px, 100px);' });
+    scrollDiv.appendChild(targetDiv);
+
+    const animation = targetDiv.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'CSS animation on an out-of-view element with pre-transform should be ' +
+       'throttled.');
+
+    await ensureElementRemoval(scrollDiv);
+  });
+
+  add_task(
+    async function throttling_animations_in_out_of_view_position_absolute_element() {
+      const parentDiv = addDiv(null,
+                             { style: 'position: absolute; top: -1000px;' });
+      const targetDiv = addDiv(null,
+                             { style: 'animation: on-main-thread 100s;' });
+      parentDiv.appendChild(targetDiv);
+
+      const animation = targetDiv.getAnimations()[0];
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+      is(markers.length, 0,
+         'CSS animation in an out-of-view position absolute element should ' +
+         'be throttled');
+
+      await ensureElementRemoval(parentDiv);
+    }
+  );
+
+  add_task(
+    async function throttling_animations_on_out_of_view_position_absolute_element() {
+      const div = addDiv(null,
+                       { style: 'animation: on-main-thread 100s; ' +
+                                'position: absolute; top: -1000px;' });
+
+      const animation = div.getAnimations()[0];
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+      is(markers.length, 0,
+         'CSS animation on an out-of-view position absolute element should ' +
+         'be throttled');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(
+    async function throttling_animations_in_out_of_view_position_fixed_element() {
+      const parentDiv = addDiv(null,
+                             { style: 'position: fixed; top: -1000px;' });
+      const targetDiv = addDiv(null,
+                             { style: 'animation: on-main-thread 100s;' });
+      parentDiv.appendChild(targetDiv);
+
+      const animation = targetDiv.getAnimations()[0];
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+      is(markers.length, 0,
+         'CSS animation on an out-of-view position:fixed element should be ' +
+         'throttled');
+
+      await ensureElementRemoval(parentDiv);
+    }
+  );
+
+  add_task(
+    async function throttling_animations_on_out_of_view_position_fixed_element() {
+      const div = addDiv(null,
+                       { style: 'animation: on-main-thread 100s; ' +
+                                'position: fixed; top: -1000px;' });
+
+      const animation = div.getAnimations()[0];
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+      is(markers.length, 0,
+         'CSS animation on an out-of-view position:fixed element should be ' +
+         'throttled');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(
+    async function no_throttling_animations_in_view_position_fixed_element() {
+      const iframe = document.createElement('iframe');
+      iframe.setAttribute('srcdoc', '<div id="target"></div>');
+      document.documentElement.appendChild(iframe);
+
+      await new Promise(resolve => {
+        iframe.addEventListener('load', () => {
+          resolve();
+        });
+      });
+
+      const target = iframe.contentDocument.getElementById('target');
+      target.style= 'position: fixed; top: 20px; width: 100px; height: 100px;';
+
+      const animation = target.animate({ zIndex: [ '0', '999' ] },
+                                       { duration: 100 * MS_PER_SEC,
+                                         iterations: Infinity });
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStylingInTargetWindow(iframe.contentWindow, 5);
+      is(markers.length, 5,
+         'CSS animation on an in-view position:fixed element should NOT be ' +
+         'throttled');
+
+      await ensureElementRemoval(iframe);
+    }
+  );
+
+  add_task(
+    async function throttling_position_absolute_animations_in_collapsed_iframe() {
+      const iframe = document.createElement('iframe');
+      iframe.setAttribute('srcdoc', '<div id="target"></div>');
+      iframe.style.height = '0px';
+      document.documentElement.appendChild(iframe);
+
+      await new Promise(resolve => {
+        iframe.addEventListener('load', () => {
+          resolve();
+        });
+      });
+
+      const target = iframe.contentDocument.getElementById("target");
+      target.style= 'position: absolute; top: 50%; width: 100px; height: 100px';
+
+      const animation = target.animate({ opacity: [0, 1] },
+                                     { duration: 100 * MS_PER_SEC,
+                                       iterations: Infinity });
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStylingInTargetWindow(iframe.contentWindow, 5);
+      is(markers.length, 0,
+         'Animation on position:absolute element in collapsed iframe should ' +
+         'be throttled');
+
+      await ensureElementRemoval(iframe);
+    }
+  );
+
+  add_task(
+    async function position_absolute_animations_in_collapsed_element() {
+      const parent = addDiv(null, { style: 'overflow: scroll; height: 0px;' });
+      const target = addDiv(null,
+                          { style: 'animation: on-main-thread 100s infinite;' +
+                                   'position: absolute; top: 50%;' +
+                                   'width: 100px; height: 100px;' });
+      parent.appendChild(target);
+
+      const animation = target.getAnimations()[0];
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+      is(markers.length, 5,
+         'Animation on position:absolute element in collapsed element ' +
+         'should not be throttled');
+
+      await ensureElementRemoval(parent);
+    }
+  );
+
+  add_task(
+    async function throttling_position_absolute_animations_in_collapsed_element() {
+      const parent = addDiv(null, { style: 'overflow: scroll; height: 0px;' });
+      const target = addDiv(null,
+                          { style: 'animation: on-main-thread 100s infinite;' +
+                                   'position: absolute; top: 50%;' });
+      parent.appendChild(target);
+
+      const animation = target.getAnimations()[0];
+      await waitForAnimationReadyToRestyle(animation);
+
+      const markers = await observeStyling(5);
+      todo_is(markers.length, 0,
+              'Animation on collapsed position:absolute element in collapsed ' +
+              'element should be throttled');
+
+      await ensureElementRemoval(parent);
+    }
+  );
+
+  add_task_if_omta_enabled(
+    async function no_restyling_for_compositor_animation_on_unrelated_style_change() {
+      const div = addDiv(null);
+      const animation = div.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+
+      await waitForAnimationReadyToRestyle(animation);
+      ok(SpecialPowers.wrap(animation).isRunningOnCompositor,
+         'The opacity animation is running on the compositor');
+
+      div.style.setProperty('color', 'blue', '');
+      const markers = await observeStyling(5);
+      is(markers.length, 0,
+         'The opacity animation keeps running on the compositor when ' +
+         'color style is changed');
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(
+    async function no_overflow_transform_animations_in_scrollable_element() {
+      const parentElement = addDiv(null,
+        { style: 'overflow-y: scroll; height: 100px;' });
+      const div = addDiv(null);
+      const animation =
+        div.animate({ transform: [ 'translateY(10px)', 'translateY(10px)' ] },
+                    100 * MS_PER_SEC);
+      parentElement.appendChild(div);
+
+      await waitForAnimationReadyToRestyle(animation);
+      ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+      const markers = await observeStyling(20);
+      is(markers.length, 0,
+         'No-overflow transform animations running on the compositor should ' +
+         'never update style on the main thread');
+
+      await ensureElementRemoval(parentElement);
+    }
+  );
+
+  add_task(async function no_flush_on_getAnimations() {
+    const div = addDiv(null);
+    const animation =
+      div.animate({ opacity: [ '0', '1' ] }, 100 * MS_PER_SEC);
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = observeAnimSyncStyling(() => {
+      is(div.getAnimations().length, 1, 'There should be one animation');
+    });
+    is(markers.length, 0,
+       'Element.getAnimations() should not flush throttled animation style');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_for_throttled_animation_on_getAnimations() {
+    const div = addDiv(null, { style: 'animation: opacity 100s' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = observeAnimSyncStyling(() => {
+      div.style.animationDuration = '0s';
+      is(div.getAnimations().length, 0, 'There should be no animation');
+    });
+
+    is(markers.length, 1, // For discarding the throttled animation.
+       'Element.getAnimations() should flush throttled animation style so ' +
+       'that the throttled animation is discarded');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(
+    async function no_restyling_for_throttled_animation_on_querying_play_state() {
+      const div = addDiv(null, { style: 'animation: opacity 100s' });
+      const animation = div.getAnimations()[0];
+      const sibling = addDiv(null);
+
+      await waitForAnimationReadyToRestyle(animation);
+      ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+      const markers = observeAnimSyncStyling(() => {
+        sibling.style.opacity = '0.5';
+        is(animation.playState, 'running',
+           'Animation.playState should be running');
+      });
+      is(markers.length, 0,
+         'Animation.playState should not flush throttled animation in the ' +
+         'case where there are only style changes that don\'t affect the ' +
+         'throttled animation');
+
+      await ensureElementRemoval(div);
+      await ensureElementRemoval(sibling);
+    }
+  );
+
+  add_task(
+    async function restyling_for_throttled_animation_on_querying_play_state() {
+      const div = addDiv(null, { style: 'animation: opacity 100s' });
+      const animation = div.getAnimations()[0];
+
+      await waitForAnimationReadyToRestyle(animation);
+      ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+      const markers = observeAnimSyncStyling(() => {
+        div.style.animationPlayState = 'paused';
+        is(animation.playState, 'paused',
+           'Animation.playState should be reflected by pending style');
+      });
+
+      is(markers.length, 1,
+         'Animation.playState should flush throttled animation style that ' +
+         'affects the throttled animation');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(
+    async function no_restyling_for_throttled_transition_on_querying_play_state() {
+      const div = addDiv(null, { style: 'transition: opacity 100s; opacity: 0' });
+      const sibling = addDiv(null);
+
+      getComputedStyle(div).opacity;
+      div.style.opacity = 1;
+
+      const transition = div.getAnimations()[0];
+
+      await waitForAnimationReadyToRestyle(transition);
+      ok(SpecialPowers.wrap(transition).isRunningOnCompositor);
+
+      const markers = observeAnimSyncStyling(() => {
+        sibling.style.opacity = '0.5';
+        is(transition.playState, 'running',
+           'Animation.playState should be running');
+      });
+
+      is(markers.length, 0,
+         'Animation.playState should not flush throttled transition in the ' +
+         'case where there are only style changes that don\'t affect the ' +
+         'throttled animation');
+
+      await ensureElementRemoval(div);
+      await ensureElementRemoval(sibling);
+    }
+  );
+
+  add_task(
+    async function restyling_for_throttled_transition_on_querying_play_state() {
+      const div = addDiv(null, { style: 'transition: opacity 100s; opacity: 0' });
+      getComputedStyle(div).opacity;
+      div.style.opacity = '1';
+
+      const transition = div.getAnimations()[0];
+
+      await waitForAnimationReadyToRestyle(transition);
+      ok(SpecialPowers.wrap(transition).isRunningOnCompositor);
+
+      const markers = observeAnimSyncStyling(() => {
+        div.style.transitionProperty = 'none';
+        is(transition.playState, 'idle',
+           'Animation.playState should be reflected by pending style change ' +
+           'which cancel the transition');
+      });
+
+      is(markers.length, 1,
+         'Animation.playState should flush throttled transition style that ' +
+         'affects the throttled animation');
+
+      await ensureElementRemoval(div);
+    }
+  );
+
+  add_task(async function restyling_visibility_animations_on_in_view_element() {
+    const div = addDiv(null);
+    const animation =
+      div.animate({ visibility: ['hidden', 'visible'] }, 100 * MS_PER_SEC);
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 5,
+       'Visibility animation running on the main-thread on in-view element ' +
+       'should not be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_outline_offset_animations_on_invisible_element() {
+    const div = addDiv(null,
+                       { style: 'visibility: hidden; ' +
+                                'outline-style: solid; ' +
+                                'outline-width: 1px;' });
+    const animation =
+      div.animate({ outlineOffset: [ '0px', '10px' ] },
+                  { duration: 100 * MS_PER_SEC,
+                    iterations: Infinity });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Outline offset animation running on the main-thread on invisible ' +
+       'element should be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_transform_animations_on_invisible_element() {
+    const div = addDiv(null, { style: 'visibility: hidden;' });
+
+    const animation =
+      div.animate({ transform: [ 'none', 'rotate(360deg)' ] },
+                  { duration: 100 * MS_PER_SEC,
+                    iterations: Infinity });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Transform animations on visibility hidden element should be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_transform_animations_on_invisible_element() {
+    const div = addDiv(null, { style: 'visibility: hidden;' });
+
+    const animation =
+      div.animate([ { transform: 'rotate(360deg)' } ],
+                  { duration: 100 * MS_PER_SEC,
+                    iterations: Infinity });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Transform animations without 100% keyframe on visibility hidden ' +
+       'element should be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_translate_animations_on_invisible_element() {
+    const div = addDiv(null, { style: 'visibility: hidden;' });
+
+    const animation =
+      div.animate([ { translate: '100px' } ],
+                  { duration: 100 * MS_PER_SEC,
+                    iterations: Infinity });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Translate animations without 100% keyframe on visibility hidden ' +
+       'element should be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_rotate_animations_on_invisible_element() {
+    const div = addDiv(null, { style: 'visibility: hidden;' });
+
+    const animation =
+      div.animate([ { rotate: '45deg' } ],
+                  { duration: 100 * MS_PER_SEC,
+                    iterations: Infinity });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Rotate animations without 100% keyframe on visibility hidden ' +
+       'element should be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_scale_animations_on_invisible_element() {
+    const div = addDiv(null, { style: 'visibility: hidden;' });
+
+    const animation =
+      div.animate([ { scale: '2 2' } ],
+                  { duration: 100 * MS_PER_SEC,
+                    iterations: Infinity });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Scale animations without 100% keyframe on visibility hidden ' +
+       'element should be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  add_task(
+    async function restyling_transform_animations_having_abs_pos_child_on_invisible_element() {
+      const div = addDiv(null, { style: 'visibility: hidden;' });
+      const child = addDiv(null, { style: 'position: absolute; top: 100px;' });
+      div.appendChild(child);
+
+      const animation =
+        div.animate({ transform: [ 'none',  'rotate(360deg)' ] },
+                    { duration: 100 * MS_PER_SEC,
+                      iterations: Infinity });
+
+      await waitForAnimationReadyToRestyle(animation);
+
+      ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+      const markers = await observeStyling(5);
+
+      is(markers.length, 0,
+         'Transform animation having an absolutely positioned child on ' +
+         'visibility hidden element should be throttled');
+      await ensureElementRemoval(div);
+  });
+
+  add_task(async function no_restyling_animations_in_out_of_view_iframe() {
+    const div = addDiv(null, { style: 'overflow-y: scroll; height: 100px;' });
+
+    const iframe = document.createElement('iframe');
+    iframe.setAttribute(
+      'srcdoc',
+      '<div style="height: 100px;"></div><div id="target"></div>');
+    div.appendChild(iframe);
+
+    await new Promise(resolve => {
+      iframe.addEventListener('load', () => {
+        resolve();
+      });
+    });
+
+    const target = iframe.contentDocument.getElementById("target");
+    target.style= 'width: 100px; height: 100px;';
+
+    const animation = target.animate({ zIndex: [ '0', '999' ] },
+                                     100 * MS_PER_SEC);
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStylingInTargetWindow(iframe.contentWindow, 5);
+    is(markers.length, 0,
+       'Animation in out-of-view iframe should be throttled');
+
+    await ensureElementRemoval(div);
+  });
+
+  // Tests that transform animations are not able to run on the compositor due
+  // to layout restrictions (e.g. animations on a large size frame) doesn't
+  // flush layout at all.
+  add_task(async function flush_layout_for_transform_animations() {
+    // Set layout.animation.prerender.partial to disallow transform animations
+    // on large frames to be sent to the compositor.
+    await SpecialPowers.pushPrefEnv({
+      set: [['layout.animation.prerender.partial', false]] });
+    const div = addDiv(null, { style: 'width: 10000px; height: 10000px;' });
+
+    const animation = div.animate([ { transform: 'rotate(360deg)', } ],
+                                  { duration: 100 * MS_PER_SEC,
+                                    // Set step-end to skip further restyles.
+                                    easing: 'step-end' });
+
+    const FLUSH_LAYOUT = SpecialPowers.DOMWindowUtils.FLUSH_LAYOUT;
+    ok(SpecialPowers.DOMWindowUtils.needsFlush(FLUSH_LAYOUT),
+       'Flush is needed for the appended div');
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor, "Shouldn't be running in the compositor");
+
+    // We expect one restyle from the initial animation compose.
+    await waitForNextFrame();
+
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor, "Still shouldn't be running in the compositor");
+    ok(!SpecialPowers.DOMWindowUtils.needsFlush(FLUSH_LAYOUT),
+       'No further layout flush needed');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function partial_prerendered_transform_animations() {
+    await SpecialPowers.pushPrefEnv({
+      set: [['layout.animation.prerender.partial', true]] });
+    const div = addDiv(null, { style: 'width: 10000px; height: 10000px;' });
+
+    const animation = div.animate(
+      // Use the same value both for `from` and `to` to avoid jank on the
+      // compositor.
+      { transform: ['rotate(0deg)', 'rotate(0deg)'] },
+      100 * MS_PER_SEC
+    );
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Transform animation with partial pre-rendered should never cause ' +
+       'restyles');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function restyling_on_create_animation() {
+    const div = addDiv();
+    const docShell = getDocShellForObservingRestylesForWindow(window);
+
+    const animationA = div.animate(
+      { transform: ['none', 'rotate(360deg)'] },
+      100 * MS_PER_SEC
+    );
+    const animationB = div.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+    const animationC = div.animate(
+      { color: ['blue', 'green'] },
+      100 * MS_PER_SEC
+    );
+    const animationD = div.animate(
+      { width: ['100px', '200px'] },
+      100 * MS_PER_SEC
+    );
+    const animationE = div.animate(
+      { height: ['100px', '200px'] },
+      100 * MS_PER_SEC
+    );
+
+    const markers = docShell
+      .popProfileTimelineMarkers()
+      .filter(marker => marker.name === 'Styles' && !marker.isAnimationOnly);
+    docShell.recordProfileTimelineMarkers = false;
+
+    is(markers.length, 0, 'Creating animations should not flush styles');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task(async function out_of_view_background_position() {
+    const div = addDiv(null, {
+      style: `
+        background-image: linear-gradient(90deg, rgb(224, 224, 224), rgb(241, 241, 241) 30%, rgb(224, 224, 224) 60%);
+        background-size: 80px;
+        animation: background-position 100s infinite;
+        transform: translateY(-400px);
+      `,
+    })
+
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0, 'background-position animations can be throttled');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_animations_in_opacity_zero_element() {
+    const div = addDiv(null, { style: 'animation: on-main-thread 100s infinite; opacity: 0' });
+    const animation = div.getAnimations()[0];
+
+    await waitForAnimationReadyToRestyle(animation);
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'Animations running on the main thread in opacity: 0 element ' +
+       'should never cause restyles');
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_compositor_animations_in_opacity_zero_descendant() {
+    const container = addDiv(null, { style: 'opacity: 0' });
+    const child = addDiv(null, { style: 'animation: background-color 100s infinite;' });
+    container.appendChild(child);
+
+    const animation = child.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the compositor in opacity zero descendant element ' +
+       'should never cause restyles');
+    await ensureElementRemoval(container);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_compositor_animations_in_opacity_zero_descendant_abspos() {
+    const container = addDiv(null, { style: 'opacity: 0' });
+    const child = addDiv(null, { style: 'position: absolute; animation: background-color 100s infinite;' });
+    container.appendChild(child);
+
+    const animation = child.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the compositor in opacity zero abspos descendant element ' +
+       'should never cause restyles');
+    await ensureElementRemoval(container);
+  });
+
+  add_task_if_omta_enabled(async function no_restyling_compositor_animations_in_opacity_zero_element() {
+    const child = addDiv(null, { style: 'animation: background-color 100s infinite; opacity: 0' });
+
+    const animation = child.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+    ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the compositor in opacity zero element ' +
+       'should never cause restyles');
+    await ensureElementRemoval(child);
+  });
+
+  add_task_if_omta_enabled(async function restyling_main_thread_animations_in_opacity_zero_descendant_after_root_opacity_animation() {
+    const container = addDiv(null, { style: 'opacity: 0' });
+
+    const child = addDiv(null, { style: 'animation: on-main-thread 100s infinite;' });
+    container.appendChild(child);
+
+    // Animate the container from 1 to zero opacity and ensure the child animation is throttled then.
+    const containerAnimation = container.animate({ opacity: [ '1', '0' ] }, 100);
+    await containerAnimation.finished;
+
+    const animation = child.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Animations running on the compositor in opacity zero descendant element ' +
+       'should never cause restyles after root animation has finished');
+    await ensureElementRemoval(container);
+  });
+
+  add_task_if_omta_enabled(async function restyling_main_thread_animations_in_opacity_zero_descendant_during_root_opacity_animation() {
+    const container = addDiv(null, { style: 'opacity: 0; animation: opacity 100s infinite' });
+
+    const child = addDiv(null, { style: 'animation: on-main-thread 100s infinite;' });
+    container.appendChild(child);
+
+    const animation = child.getAnimations()[0];
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 5,
+       'Animations in opacity zero descendant element ' +
+       'should not be throttled if root is animating opacity');
+    await ensureElementRemoval(container);
+  });
+
+  add_task_if_omta_enabled(async function transparent_background_color_animations() {
+    const div = addDiv(null);
+    const animation =
+      div.animate({ backgroundColor: [ 'rgb(0, 200, 0, 0)',
+                                       'rgb(200, 0, 0, 0.1)' ] },
+                  { duration: 100 * MS_PER_SEC,
+                    // An easing function producing zero in the first half of
+                    // the duration.
+                    easing: 'cubic-bezier(1, 0, 1, 0)' });
+    await waitForAnimationReadyToRestyle(animation);
+
+    ok(SpecialPowers.wrap(animation).isRunningOnCompositor);
+
+    const markers = await observeStyling(5);
+    is(markers.length, 0,
+       'transparent background-color animation should not update styles on ' +
+       'the main thread');
+
+    await ensureElementRemoval(div);
+  });
+
+  add_task_if_omta_enabled(async function transform_animation_on_collapsed_element() {
+    const iframe = document.createElement('iframe');
+    document.body.appendChild(iframe);
+
+    // Load a cross origin iframe.
+    const targetURL = SimpleTest.getTestFileURL("empty.html")
+      .replace(window.location.origin, "http://example.com/");
+    iframe.src = targetURL;
+    await new Promise(resolve => {
+      iframe.onload = resolve;
+    });
+
+    await SpecialPowers.spawn(iframe, [MS_PER_SEC], async (MS_PER_SEC) => {
+      // Create a flex item with "preserve-3d" having an abs-pos child inside
+      // a grid container.
+      // These styles make the the flex item size (0x0).
+      const gridContainer = content.document.createElement("div");
+      gridContainer.style.display = "grid";
+      gridContainer.style.placeItems = "center";
+
+      const target = content.document.createElement("div");
+      target.style.display = "flex";
+      target.style.transformStyle = "preserve-3d";
+      gridContainer.appendChild(target);
+
+      const child = content.document.createElement("div");
+      child.style.position = "absolute";
+      child.style.transform = "rotateY(0deg)";
+      child.style.width = "100px";
+      child.style.height = "100px";
+      child.style.backgroundColor = "green";
+      target.appendChild(child);
+
+      content.document.body.appendChild(gridContainer);
+
+      const animation =
+        target.animate({ transform: [ "rotateY(0deg)", "rotateY(360deg)" ] },
+                    { duration: 100 * MS_PER_SEC,
+                      id: "test",
+                      easing: 'step-end' });
+      await content.wrappedJSObject.waitForAnimationReadyToRestyle(animation);
+      ok(SpecialPowers.wrap(animation).isRunningOnCompositor,
+         'transform animation on a collapsed element should run on the ' +
+         'compositor');
+
+      const markers = await content.wrappedJSObject.observeStyling(5);
+      is(markers.length, 0,
+         'transform animation on a collapsed element animation should not ' +
+         'update styles on the main thread');
+    });
+
+    await ensureElementRemoval(iframe);
+  });
+});
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/file_transition_finish_on_compositor.html b/dom/animation/test/mozilla/file_transition_finish_on_compositor.html
new file mode 100644
index 0000000000..4912d05dd1
--- /dev/null
+++ b/dom/animation/test/mozilla/file_transition_finish_on_compositor.html
@@ -0,0 +1,67 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="../testcommon.js"></script>
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<style>
+div {
+  /* Element needs geometry to be eligible for layerization */
+  width: 100px;
+  height: 100px;
+  background-color: white;
+}
+</style>
+<body>
+<script>
+'use strict';
+
+function waitForPaints() {
+  return new Promise(function(resolve, reject) {
+    waitForAllPaintsFlushed(resolve);
+  });
+}
+
+promise_test(t => {
+  // This test only applies to compositor animations
+  if (!isOMTAEnabled()) {
+    return;
+  }
+
+  var div = addDiv(t, { style: 'transition: transform 50ms; ' +
+                               'transform: translateX(0px)' });
+  getComputedStyle(div).transform;
+
+  div.style.transform = 'translateX(100px)';
+
+  var timeBeforeStart = window.performance.now();
+  return waitForPaints().then(() => {
+    // If it took over 50ms to paint the transition, we have no luck
+    // to test it.  This situation will happen if GC runs while waiting for the
+    // paint.
+    if (window.performance.now() - timeBeforeStart >= 50) {
+      return;
+    }
+
+    var transform  =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_not_equals(transform, '',
+                      'The transition style is applied on the compositor');
+
+    // Generate artificial busyness on the main thread for 100ms.
+    var timeAtStart = window.performance.now();
+    while (window.performance.now() - timeAtStart < 100) {}
+
+    // Now the transition on the compositor should finish but stay at the final
+    // position because there was no chance to pull the transition back from
+    // the compositor.
+    transform  =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_equals(transform, 'matrix(1, 0, 0, 1, 100, 0)',
+                  'The final transition style is still applied on the ' +
+                  'compositor');
+  });
+}, 'Transition on the compositor keeps the final style while the main thread ' +
+   'is busy even if the transition finished on the compositor');
+
+done();
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_cascade.html b/dom/animation/test/mozilla/test_cascade.html
new file mode 100644
index 0000000000..4bdb07530e
--- /dev/null
+++ b/dom/animation/test/mozilla/test_cascade.html
@@ -0,0 +1,37 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<style>
+@keyframes margin-left {
+  from { margin-left: 20px; }
+  to   { margin-left: 80px; }
+}
+</style>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+test(function(t) {
+  var div = addDiv(t, { style: 'transition: margin-left 100s; ' +
+                               'margin-left: 80px' });
+  var cs = getComputedStyle(div);
+
+  assert_equals(cs.marginLeft, '80px', 'initial margin-left');
+
+  div.style.marginLeft = "20px";
+  assert_equals(cs.marginLeft, '80px', 'margin-left transition at 0s');
+
+  div.style.animation = "margin-left 2s";
+  assert_equals(cs.marginLeft, '20px',
+                'margin-left animation overrides transition at 0s');
+
+  div.style.animation = "none";
+  assert_equals(cs.marginLeft, '80px',
+                'margin-left animation stops overriding transition at 0s');
+}, 'Animation overrides/stops overriding transition immediately');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_cubic_bezier_limits.html b/dom/animation/test/mozilla/test_cubic_bezier_limits.html
new file mode 100644
index 0000000000..bdbc78654f
--- /dev/null
+++ b/dom/animation/test/mozilla/test_cubic_bezier_limits.html
@@ -0,0 +1,168 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<body>
+<style>
+@keyframes anim {
+  to { margin-left: 100px; }
+}
+
+.transition-div {
+  margin-left: 100px;
+}
+</style>
+<div id="log"></div>
+<script>
+'use strict';
+
+// We clamp +infinity or -inifinity value in floating point to
+// maximum floating point value or -maxinum floating point value.
+const max_float = '3.40282e38';
+
+test(function(t) {
+  var div = addDiv(t);
+  var anim = div.animate({ }, 100 * MS_PER_SEC);
+
+  anim.effect.updateTiming({ easing: 'cubic-bezier(0, 1e+39, 0, 0)' });
+  assert_equals(anim.effect.getComputedTiming().easing,
+    'cubic-bezier(0, ' + max_float + ', 0, 0)',
+    'y1 control point for effect easing is out of upper boundary');
+
+  anim.effect.updateTiming({ easing: 'cubic-bezier(0, 0, 0, 1e+39)' });
+  assert_equals(anim.effect.getComputedTiming().easing,
+    'cubic-bezier(0, 0, 0, ' + max_float + ')',
+    'y2 control point for effect easing is out of upper boundary');
+
+  anim.effect.updateTiming({ easing: 'cubic-bezier(0, -1e+39, 0, 0)' });
+  assert_equals(anim.effect.getComputedTiming().easing,
+    'cubic-bezier(0, ' + '-' + max_float + ', 0, 0)',
+    'y1 control point for effect easing is out of lower boundary');
+
+  anim.effect.updateTiming({ easing: 'cubic-bezier(0, 0, 0, -1e+39)' });
+  assert_equals(anim.effect.getComputedTiming().easing,
+    'cubic-bezier(0, 0, 0, ' + '-' + max_float + ')',
+    'y2 control point for effect easing is out of lower boundary');
+
+}, 'Clamp y1 and y2 control point out of boundaries for effect easing' );
+
+test(function(t) {
+  var div = addDiv(t);
+  var anim = div.animate({ }, 100 * MS_PER_SEC);
+
+  anim.effect.setKeyframes([ { easing: 'cubic-bezier(0, 1e+39, 0, 0)' }]);
+  assert_equals(anim.effect.getKeyframes()[0].easing,
+    'cubic-bezier(0, ' + max_float + ', 0, 0)',
+    'y1 control point for keyframe easing is out of upper boundary');
+
+  anim.effect.setKeyframes([ { easing: 'cubic-bezier(0, 0, 0, 1e+39)' }]);
+  assert_equals(anim.effect.getKeyframes()[0].easing,
+    'cubic-bezier(0, 0, 0, ' + max_float + ')',
+    'y2 control point for keyframe easing is out of upper boundary');
+
+  anim.effect.setKeyframes([ { easing: 'cubic-bezier(0, -1e+39, 0, 0)' }]);
+  assert_equals(anim.effect.getKeyframes()[0].easing,
+    'cubic-bezier(0, ' + '-' + max_float + ', 0, 0)',
+    'y1 control point for keyframe easing is out of lower boundary');
+
+  anim.effect.setKeyframes([ { easing: 'cubic-bezier(0, 0, 0, -1e+39)' }]);
+  assert_equals(anim.effect.getKeyframes()[0].easing,
+    'cubic-bezier(0, 0, 0, ' + '-' + max_float + ')',
+    'y2 control point for keyframe easing is out of lower boundary');
+
+}, 'Clamp y1 and y2 control point out of boundaries for keyframe easing' );
+
+test(function(t) {
+  var div = addDiv(t);
+
+  div.style.animation = 'anim 100s cubic-bezier(0, 1e+39, 0, 0)';
+
+  assert_equals(div.getAnimations()[0].effect.getKeyframes()[0].easing,
+    'cubic-bezier(0, ' + max_float + ', 0, 0)',
+    'y1 control point for CSS animation is out of upper boundary');
+
+  div.style.animation = 'anim 100s cubic-bezier(0, 0, 0, 1e+39)';
+  assert_equals(div.getAnimations()[0].effect.getKeyframes()[0].easing,
+    'cubic-bezier(0, 0, 0, ' + max_float + ')',
+    'y2 control point for CSS animation is out of upper boundary');
+
+  div.style.animation = 'anim 100s cubic-bezier(0, -1e+39, 0, 0)';
+  assert_equals(div.getAnimations()[0].effect.getKeyframes()[0].easing,
+    'cubic-bezier(0, ' + '-' + max_float + ', 0, 0)',
+    'y1 control point for CSS animation is out of lower boundary');
+
+  div.style.animation = 'anim 100s cubic-bezier(0, 0, 0, -1e+39)';
+  assert_equals(div.getAnimations()[0].effect.getKeyframes()[0].easing,
+    'cubic-bezier(0, 0, 0, ' + '-' + max_float + ')',
+    'y2 control point for CSS animation is out of lower boundary');
+
+}, 'Clamp y1 and y2 control point out of boundaries for CSS animation' );
+
+test(function(t) {
+  var div = addDiv(t, {'class': 'transition-div'});
+
+  div.style.transition = 'margin-left 100s cubic-bezier(0, 1e+39, 0, 0)';
+  flushComputedStyle(div);
+  div.style.marginLeft = '0px';
+  assert_equals(div.getAnimations()[0].effect.getTiming().easing,
+    'cubic-bezier(0, ' + max_float + ', 0, 0)',
+    'y1 control point for CSS transition on upper boundary');
+  div.style.transition = '';
+  div.style.marginLeft = '';
+
+  div.style.transition = 'margin-left 100s cubic-bezier(0, 0, 0, 1e+39)';
+  flushComputedStyle(div);
+  div.style.marginLeft = '0px';
+  assert_equals(div.getAnimations()[0].effect.getTiming().easing,
+    'cubic-bezier(0, 0, 0, ' + max_float + ')',
+    'y2 control point for CSS transition on upper boundary');
+  div.style.transition = '';
+  div.style.marginLeft = '';
+
+  div.style.transition = 'margin-left 100s cubic-bezier(0, -1e+39, 0, 0)';
+  flushComputedStyle(div);
+  div.style.marginLeft = '0px';
+  assert_equals(div.getAnimations()[0].effect.getTiming().easing,
+    'cubic-bezier(0, ' + '-' + max_float + ', 0, 0)',
+    'y1 control point for CSS transition on lower boundary');
+  div.style.transition = '';
+  div.style.marginLeft = '';
+
+  div.style.transition = 'margin-left 100s cubic-bezier(0, 0, 0, -1e+39)';
+  flushComputedStyle(div);
+  div.style.marginLeft = '0px';
+  assert_equals(div.getAnimations()[0].effect.getTiming().easing,
+    'cubic-bezier(0, 0, 0, ' + '-' + max_float + ')',
+    'y2 control point for CSS transition on lower boundary');
+
+}, 'Clamp y1 and y2 control point out of boundaries for CSS transition' );
+
+test(function(t) {
+  var div = addDiv(t);
+  var anim = div.animate({ }, { duration: 100 * MS_PER_SEC, fill: 'forwards' });
+
+  anim.pause();
+  // The positive steepest function on both edges.
+  anim.effect.updateTiming({ easing: 'cubic-bezier(0, 1e+39, 0, 1e+39)' });
+  assert_equals(anim.effect.getComputedTiming().progress, 0.0,
+    'progress on lower edge for the highest value of y1 and y2 control points');
+
+  anim.finish();
+  assert_equals(anim.effect.getComputedTiming().progress, 1.0,
+    'progress on upper edge for the highest value of y1 and y2 control points');
+
+  // The negative steepest function on both edges.
+  anim.effect.updateTiming({ easing: 'cubic-bezier(0, -1e+39, 0, -1e+39)' });
+  anim.currentTime = 0;
+  assert_equals(anim.effect.getComputedTiming().progress, 0.0,
+    'progress on lower edge for the lowest value of y1 and y2 control points');
+
+  anim.finish();
+  assert_equals(anim.effect.getComputedTiming().progress, 1.0,
+    'progress on lower edge for the lowest value of y1 and y2 control points');
+
+}, 'Calculated values on both edges');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_deferred_start.html b/dom/animation/test/mozilla/test_deferred_start.html
new file mode 100644
index 0000000000..7d0a15b1f7
--- /dev/null
+++ b/dom/animation/test/mozilla/test_deferred_start.html
@@ -0,0 +1,21 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+setup({explicit_done: true});
+SpecialPowers.pushPrefEnv(
+  {
+    set: [
+      ["dom.animations-api.core.enabled", true],
+      ["dom.animations-api.getAnimations.enabled", true],
+      ["dom.animations-api.timelines.enabled", true],
+    ],
+  },
+  function() {
+    window.open("file_deferred_start.html");
+  }
+);
+</script>
diff --git a/dom/animation/test/mozilla/test_disable_animations_api_autoremove.html b/dom/animation/test/mozilla/test_disable_animations_api_autoremove.html
new file mode 100644
index 0000000000..56e6362273
--- /dev/null
+++ b/dom/animation/test/mozilla/test_disable_animations_api_autoremove.html
@@ -0,0 +1,15 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+setup({ explicit_done: true });
+SpecialPowers.pushPrefEnv(
+  { set: [['dom.animations-api.autoremove.enabled', false]] },
+  function() {
+    window.open('file_disable_animations_api_autoremove.html');
+  }
+);
+</script>
diff --git a/dom/animation/test/mozilla/test_disable_animations_api_compositing.html b/dom/animation/test/mozilla/test_disable_animations_api_compositing.html
new file mode 100644
index 0000000000..94216ea62d
--- /dev/null
+++ b/dom/animation/test/mozilla/test_disable_animations_api_compositing.html
@@ -0,0 +1,14 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+setup({explicit_done: true});
+SpecialPowers.pushPrefEnv(
+  { "set": [["dom.animations-api.compositing.enabled", false]]},
+  function() {
+    window.open("file_disable_animations_api_compositing.html");
+  });
+</script>
diff --git a/dom/animation/test/mozilla/test_disable_animations_api_get_animations.html b/dom/animation/test/mozilla/test_disable_animations_api_get_animations.html
new file mode 100644
index 0000000000..a7253439b7
--- /dev/null
+++ b/dom/animation/test/mozilla/test_disable_animations_api_get_animations.html
@@ -0,0 +1,14 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+setup({explicit_done: true});
+SpecialPowers.pushPrefEnv(
+  { "set": [["dom.animations-api.getAnimations.enabled", false]]},
+  function() {
+    window.open("file_disable_animations_api_get_animations.html");
+  });
+</script>
diff --git a/dom/animation/test/mozilla/test_disable_animations_api_implicit_keyframes.html b/dom/animation/test/mozilla/test_disable_animations_api_implicit_keyframes.html
new file mode 100644
index 0000000000..aaebf1f00a
--- /dev/null
+++ b/dom/animation/test/mozilla/test_disable_animations_api_implicit_keyframes.html
@@ -0,0 +1,14 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+setup({explicit_done: true});
+SpecialPowers.pushPrefEnv(
+  { "set": [["dom.animations-api.implicit-keyframes.enabled", false]]},
+  function() {
+    window.open("file_disable_animations_api_implicit_keyframes.html");
+  });
+</script>
diff --git a/dom/animation/test/mozilla/test_disable_animations_api_timelines.html b/dom/animation/test/mozilla/test_disable_animations_api_timelines.html
new file mode 100644
index 0000000000..a20adf4ea2
--- /dev/null
+++ b/dom/animation/test/mozilla/test_disable_animations_api_timelines.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+
+setup({ explicit_done: true });
+SpecialPowers.pushPrefEnv(
+  { set: [['dom.animations-api.timelines.enabled', false]] },
+  function() {
+    window.open('file_disable_animations_api_timelines.html');
+  }
+);
+</script>
diff --git a/dom/animation/test/mozilla/test_disabled_properties.html b/dom/animation/test/mozilla/test_disabled_properties.html
new file mode 100644
index 0000000000..2244143ceb
--- /dev/null
+++ b/dom/animation/test/mozilla/test_disabled_properties.html
@@ -0,0 +1,73 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+function waitForSetPref(pref, value) {
+  return SpecialPowers.pushPrefEnv({ 'set': [[pref, value]] });
+}
+
+/*
+ * These tests rely on the fact that the overflow-clip-box property is
+ * disabled by the layout.css.overflow-clip-box.enabled pref. If we ever remove
+ * that pref we will need to substitute some other pref:property combination.
+ */
+
+promise_test(function(t) {
+  return waitForSetPref('layout.css.overflow-clip-box.enabled', true).then(() => {
+    var anim = addDiv(t).animate({ overflowClipBoxBlock: [ 'padding-box', 'content-box' ]});
+    assert_equals(anim.effect.getKeyframes().length, 2,
+                  'A property-indexed keyframe specifying only enabled'
+                  + ' properties produces keyframes');
+    return waitForSetPref('layout.css.overflow-clip-box.enabled', false);
+  }).then(() => {
+    var anim = addDiv(t).animate({ overflowClipBoxBlock: [ 'padding-box', 'content-box' ]});
+    assert_equals(anim.effect.getKeyframes().length, 0,
+                  'A property-indexed keyframe specifying only disabled'
+                  + ' properties produces no keyframes');
+  });
+}, 'Specifying a disabled property using a property-indexed keyframe');
+
+promise_test(function(t) {
+  var createAnim = () => {
+    var anim = addDiv(t).animate([ { overflowClipBoxBlock: 'padding-box' },
+                                   { overflowClipBoxBlock: 'content-box' } ]);
+    assert_equals(anim.effect.getKeyframes().length, 2,
+                  'Animation specified using a keyframe sequence should'
+                  + ' return the same number of keyframes regardless of'
+                  + ' whether or not the specified properties are disabled');
+    return anim;
+  };
+
+  var assert_has_property = (anim, index, descr, property) => {
+    assert_true(
+      anim.effect.getKeyframes()[index].hasOwnProperty(property),
+      `${descr} should have the '${property}' property`);
+  };
+  var assert_does_not_have_property = (anim, index, descr, property) => {
+    assert_false(
+      anim.effect.getKeyframes()[index].hasOwnProperty(property),
+      `${descr} should NOT have the '${property}' property`);
+  };
+
+  return waitForSetPref('layout.css.overflow-clip-box.enabled', true).then(() => {
+    var anim = createAnim();
+    assert_has_property(anim, 0, 'Initial keyframe', 'overflowClipBoxBlock');
+    assert_has_property(anim, 1, 'Final keyframe', 'overflowClipBoxBlock');
+    return waitForSetPref('layout.css.overflow-clip-box.enabled', false);
+  }).then(() => {
+    var anim = createAnim();
+    assert_does_not_have_property(anim, 0, 'Initial keyframe',
+                                  'overflowClipBoxBlock');
+    assert_does_not_have_property(anim, 1, 'Final keyframe',
+                                  'overflowClipBoxBlock');
+  });
+}, 'Specifying a disabled property using a keyframe sequence');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_discrete_animations.html b/dom/animation/test/mozilla/test_discrete_animations.html
new file mode 100644
index 0000000000..d4826a74bd
--- /dev/null
+++ b/dom/animation/test/mozilla/test_discrete_animations.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+setup({explicit_done: true});
+SpecialPowers.pushPrefEnv(
+  { "set": [
+    ["layout.css.osx-font-smoothing.enabled", true],
+  ] },
+  function() {
+    window.open("file_discrete_animations.html");
+  });
+</script>
diff --git a/dom/animation/test/mozilla/test_distance_of_basic_shape.html b/dom/animation/test/mozilla/test_distance_of_basic_shape.html
new file mode 100644
index 0000000000..65e403bf06
--- /dev/null
+++ b/dom/animation/test/mozilla/test_distance_of_basic_shape.html
@@ -0,0 +1,91 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src='/resources/testharness.js'></script>
+<script src='/resources/testharnessreport.js'></script>
+<script src='../testcommon.js'></script>
+<div id='log'></div>
+<script type='text/javascript'>
+'use strict';
+
+// We don't have an official spec to define the distance between two basic
+// shapes, but we still need this for DevTools, so Gecko and Servo backends use
+// the similar rules to define the distance. If there is a spec for it, we have
+// to update this test file.
+// See https://github.com/w3c/csswg-drafts/issues/662.
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'clip-path', 'none', 'none');
+  assert_equals(dist, 0, 'none and none');
+}, 'none and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'clip-path', 'circle(10px)', 'circle(20px)');
+  assert_equals(dist, 10, 'circle(10px) and circle(20px)');
+}, 'circles');
+
+test(function(t) {
+  var target = addDiv(t);
+  var circle1 = 'circle(calc(10px + 10px) at 20px 10px)';
+  var circle2 = 'circle(30px at 10px 10px)';
+  var dist = getDistance(target, 'clip-path', circle1, circle2);
+  assert_equals(dist,
+                Math.sqrt(10 * 10 + 10 * 10),
+                circle1 + ' and ' + circle2);
+}, 'circles with positions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var ellipse1 = 'ellipse(20px calc(10px + 10px))';
+  var ellipse2 = 'ellipse(30px 30px)';
+  var dist = getDistance(target, 'clip-path', ellipse1, ellipse2);
+  assert_equals(dist,
+                Math.sqrt(10 * 10 + 10 * 10),
+                ellipse1 + ' and ' + ellipse2);
+}, 'ellipses');
+
+test(function(t) {
+  var target = addDiv(t);
+  var polygon1 = 'polygon(50px 0px, 100px 50px, 50px 100px, 0px 50px)';
+  var polygon2 = 'polygon(40px 0px, 100px 70px, 10px 100px, 0px 70px)';
+  var dist = getDistance(target, 'clip-path', polygon1, polygon2);
+  assert_equals(dist,
+                Math.sqrt(10 * 10 + 20 * 20 + 40 * 40 + 20 * 20),
+                polygon1 + ' and ' + polygon2);
+}, 'polygons');
+
+test(function(t) {
+  var target = addDiv(t);
+  var inset1 = 'inset(5px 5px 5px 5px round 40px 30px 20px 5px)';
+  var inset2 = 'inset(10px 5px round 50px 60px)';
+  var dist = getDistance(target, 'clip-path', inset1, inset2);
+
+  // if we have only two parameter in inset(), the first one means
+  // top and bottom edges, and the second one means left and right edges.
+  // and the definitions of inset is inset(top, right, bottom, left). Besides,
+  // the "round" part uses the shorthand of border radius for each corner, so
+  // each corner is a pair of (x, y). We are computing the distance between:
+  // 1. inset(5px  5px  5px 5px
+  //          round (40px 40px) (30px 30px) (20px 20px) (5px 5px))
+  // 2. inset(10px 5px 10px 5px
+  //          round (50px 50px) (60px 60px) (50px 50px) (60px 60px))
+  // That is why we need to multiply 2 for each border-radius corner.
+  assert_equals(dist,
+                Math.sqrt(5 * 5 + 5 * 5 +
+                          (50 - 40) * (50 - 40) * 2 +
+                          (60 - 30) * (60 - 30) * 2 +
+                          (50 - 20) * (50 - 20) * 2 +
+                          (60 - 5)  * (60 - 5)  * 2),
+                inset1 + ' and ' + inset2);
+}, 'insets');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'clip-path',
+                         'circle(20px)', 'ellipse(10px 20px)');
+  assert_equals(dist, 0, 'circle(20px) and ellipse(10px 20px)');
+}, 'Mismatched basic shapes');
+
+</script>
+</html>
diff --git a/dom/animation/test/mozilla/test_distance_of_filter.html b/dom/animation/test/mozilla/test_distance_of_filter.html
new file mode 100644
index 0000000000..33f772d983
--- /dev/null
+++ b/dom/animation/test/mozilla/test_distance_of_filter.html
@@ -0,0 +1,248 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src='/resources/testharness.js'></script>
+<script src='/resources/testharnessreport.js'></script>
+<script src='../testcommon.js'></script>
+<div id='log'></div>
+<script type='text/javascript'>
+'use strict';
+
+const EPSILON = 1e-6;
+
+// We don't have an official spec to define the distance between two filter
+// lists, but we still need this for DevTools, so Gecko and Servo backends use
+// the similar rules to define the distance. If there is a spec for it, we have
+// to update this test file.
+// See https://github.com/w3c/fxtf-drafts/issues/91.
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'none', 'none');
+  assert_equals(dist, 0, 'none and none');
+}, 'none and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'blur(10px)', 'none');
+  // The default value of blur is 0px.
+  assert_equals(dist, 10, 'blur(10px) and none');
+}, 'blur and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'blur(10px)', 'blur(1px)');
+  assert_equals(dist, 9, 'blur(10px) and blur(1px)');
+}, 'blurs');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'brightness(75%)', 'none');
+  // The default value of brightness is 100%.
+  assert_equals(dist, (1 - 0.75), 'brightness(75%) and none');
+}, 'brightness and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter',
+                         'brightness(50%)', 'brightness(175%)');
+  assert_equals(dist, (1.75 - 0.5), 'brightness(50%) and brightness(175%)');
+}, 'brightnesses');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'contrast(75%)', 'none');
+  // The default value of contrast is 100%.
+  assert_equals(dist, (1 - 0.75), 'contrast(75%) and none');
+}, 'contrast and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'contrast(50%)', 'contrast(175%)');
+  assert_equals(dist, (1.75 - 0.5), 'contrast(50%) and contrast(175%)');
+}, 'contrasts');
+
+test(function(t) {
+  var target = addDiv(t);
+  var filter1 = 'drop-shadow(10px 10px 10px blue)';
+  var filter2 = 'none';
+  var dist = getDistance(target, 'filter', filter1, filter2);
+  // The rgba of Blue is rgba(0, 0, 255, 1.0) = rgba(0%, 0%, 100%, 100%).
+  // So we are try to compute the distance of
+  // 1. drop-shadow(10, 10, 10, rgba(0, 0, 1.0, 1.0)).
+  // 2. drop-shadow( 0,  0,  0, rgba(0, 0, 0, 0)).
+  assert_equals(dist,
+                Math.sqrt(10 * 10 * 3 + (1 * 1 + 1 * 1)),
+                filter1 + ' and ' + filter2);
+}, 'drop-shadow and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var filter1 = 'drop-shadow(10px 10px 10px blue)';
+  var filter2 = 'drop-shadow(5px 5px 1px yellow)';
+  var dist = getDistance(target, 'filter', filter1, filter2);
+  // Blue:   rgba(0, 0, 255, 1.0)   = rgba(  0%,   0%, 100%, 100%).
+  // Yellow: rgba(255, 255, 0, 1.0) = rgba(100%, 100%,   0%, 100%).
+  assert_equals(dist,
+                Math.sqrt(5 * 5 * 2 + 9 * 9 + (1 * 1 * 3)),
+                filter1 + ' and ' + filter2);
+}, 'drop-shadows');
+
+test(function(t) {
+  var target = addDiv(t);
+  var filter1 = 'drop-shadow(10px 10px 10px)';
+  var filter2 = 'drop-shadow(5px 5px 1px yellow)';
+  var dist = getDistance(target, 'filter', filter1, filter2);
+  // Yellow:      rgba(255, 255, 0, 1.0) = rgba(100%, 100%,   0%, 100%)
+  // Transparent: rgba(0, 0, 0, 0)       = rgba(  0%,   0%,   0%,   0%)
+  // Distance involving `currentcolor` is calculated as distance
+  //   from `transparent`
+  assert_equals(dist,
+                Math.sqrt(5 * 5 * 2 + 9 * 9 + (1 * 1 * 3)),
+                filter1 + ' and ' + filter2);
+}, 'drop-shadows with color and non-color');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'grayscale(25%)', 'none');
+  // The default value of grayscale is 0%.
+  assert_equals(dist, 0.25, 'grayscale(25%) and none');
+}, 'grayscale and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'grayscale(50%)', 'grayscale(75%)');
+  assert_equals(dist, 0.25, 'grayscale(50%) and grayscale(75%)');
+}, 'grayscales');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'grayscale(75%)', 'grayscale(175%)');
+  assert_equals(dist, 0.25, 'distance of grayscale(75%) and grayscale(175%)');
+}, 'grayscales where one has a value larger than 1.0');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'hue-rotate(180deg)', 'none');
+  // The default value of hue-rotate is 0deg.
+  assert_approx_equals(dist, Math.PI, EPSILON, 'hue-rotate(180deg) and none');
+}, 'hue-rotate and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter',
+                         'hue-rotate(720deg)', 'hue-rotate(-180deg)');
+  assert_approx_equals(dist, 5 * Math.PI, EPSILON,
+                       'hue-rotate(720deg) and hue-rotate(-180deg)');
+}, 'hue-rotates');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'invert(25%)', 'none');
+  // The default value of invert is 0%.
+  assert_equals(dist, 0.25, 'invert(25%) and none');
+}, 'invert and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'invert(50%)', 'invert(75%)');
+  assert_equals(dist, 0.25, 'invert(50%) and invert(75%)');
+}, 'inverts');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'invert(75%)', 'invert(175%)');
+  assert_equals(dist, 0.25, 'invert(75%) and invert(175%)');
+}, 'inverts where one has a value larger than 1.0');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'opacity(75%)', 'none');
+  // The default value of opacity is 100%.
+  assert_equals(dist, (1 - 0.75), 'opacity(75%) and none');
+}, 'opacity and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'opacity(50%)', 'opacity(75%)');
+  assert_equals(dist, 0.25, 'opacity(50%) and opacity(75%)');
+}, 'opacities');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'opacity(75%)', 'opacity(175%)');
+  assert_equals(dist, 0.25, 'opacity(75%) and opacity(175%)');
+}, 'opacities where one has a value larger than 1.0');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'saturate(75%)', 'none');
+  // The default value of saturate is 100%.
+  assert_equals(dist, (1 - 0.75), 'saturate(75%) and none');
+}, 'saturate and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'saturate(50%)', 'saturate(175%)');
+  assert_equals(dist, (1.75 - 0.5), 'saturate(50%) and saturate(175%)');
+}, 'saturates');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'sepia(25%)', 'none');
+  // The default value of sepia is 0%.
+  assert_equals(dist, 0.25, 'sepia(25%) and none');
+}, 'sepia and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'sepia(50%)', 'sepia(75%)');
+  assert_equals(dist, 0.25, 'sepia(50%) and sepia(75%)');
+}, 'sepias');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'filter', 'sepia(75%)', 'sepia(175%)');
+  assert_equals(dist, 0.25, 'sepia(75%) and sepia(175%)');
+}, 'sepias where one has a value larger than 1.0');
+
+test(function(t) {
+  var target = addDiv(t);
+  var filter1 = 'grayscale(50%) opacity(100%) blur(5px)';
+  // none filter: 'grayscale(0) opacity(1) blur(0px)'
+  var filter2 = 'none';
+  var dist = getDistance(target, 'filter', filter1, filter2);
+  assert_equals(dist,
+                Math.sqrt(0.5 * 0.5 + 5 * 5),
+                filter1 + ' and ' + filter2);
+}, 'Filter list and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var filter1 = 'grayscale(50%) opacity(100%) blur(5px)';
+  var filter2 = 'grayscale(100%) opacity(50%) blur(1px)';
+  var dist = getDistance(target, 'filter', filter1, filter2);
+  assert_equals(dist,
+                Math.sqrt(0.5 * 0.5 + 0.5 * 0.5 + 4 * 4),
+                filter1 + ' and ' + filter2);
+}, 'Filter lists');
+
+test(function(t) {
+  var target = addDiv(t);
+  var filter1 = 'grayscale(50%) opacity(100%) blur(5px)';
+  var filter2 = 'grayscale(100%) opacity(50%) blur(1px) sepia(50%)';
+  var dist = getDistance(target, 'filter', filter1, filter2);
+  assert_equals(dist,
+                Math.sqrt(0.5 * 0.5 + 0.5 * 0.5 + 4 * 4 + 0.5 * 0.5),
+                filter1 + ' and ' + filter2);
+}, 'Filter lists where one has extra functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var filter1 = 'grayscale(50%) opacity(100%)';
+  var filter2 = 'opacity(100%) grayscale(50%)';
+  var dist = getDistance(target, 'filter', filter1, filter2);
+  assert_equals(dist, 0, filter1 + ' and ' + filter2);
+}, 'Mismatched filter lists');
+
+</script>
+</html>
diff --git a/dom/animation/test/mozilla/test_distance_of_path_function.html b/dom/animation/test/mozilla/test_distance_of_path_function.html
new file mode 100644
index 0000000000..af6592c892
--- /dev/null
+++ b/dom/animation/test/mozilla/test_distance_of_path_function.html
@@ -0,0 +1,140 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src='/resources/testharness.js'></script>
+<script src='/resources/testharnessreport.js'></script>
+<script src='../testcommon.js'></script>
+<div id="log"></div>
+<script type='text/javascript'>
+'use strict';
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path', 'none', 'none');
+  assert_equals(dist, 0, 'none and none');
+}, 'none and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path', 'path("M 10 10")', 'none');
+  assert_equals(dist, 0, 'path("M 10 10") and none');
+}, 'Path and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 10 10 H 10")',
+                         'path("M 10 10 H 10 H 10")');
+  assert_equals(dist, 0, 'path("M 10 10 H 10") and ' +
+                         'path("M 10 10 H 10 H 10")');
+}, 'Mismatched path functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 10 10")',
+                         'path("M 20 20")');
+  assert_equals(dist,
+                Math.sqrt(10 * 10 * 2),
+                'path("M 10 10") and path("M 30 30")');
+}, 'The moveto commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 0 0 L 10 10")',
+                         'path("M 0 0 L 20 20")');
+  assert_equals(dist,
+                Math.sqrt(10 * 10 * 2),
+                'path("M 0 0 L 10 10") and path("M 0 0 L 20 20")');
+}, 'The lineto commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 0 0 H 10")',
+                         'path("M 0 0 H 20")');
+  assert_equals(dist, 10, 'path("M 0 0 H 10") and path("M 0 0 H 20")');
+}, 'The horizontal lineto commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 0 0 V 10")',
+                         'path("M 0 0 V 20")');
+  assert_equals(dist, 10, 'path("M 0 0 V 10") and path("M 0 0 V 20")');
+}, 'The vertical lineto commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 0 0 C 10 10 20 20 30 30")',
+                         'path("M 0 0 C 20 20 40 40 0 0")');
+  assert_equals(dist,
+                Math.sqrt(10 * 10 * 2 + 20 * 20 * 2 + 30 * 30 * 2),
+                'path("M 0 0 C 10 10 20 20 30 30") and ' +
+                'path("M 0 0 C 20 20 40 40 0 0")');
+}, 'The cubic Bézier curve commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 0 0 S 20 20 30 30")',
+                         'path("M 0 0 S 40 40 0 0")');
+  assert_equals(dist,
+                Math.sqrt(20 * 20 * 2 + 30 * 30 * 2),
+                'path("M 0 0 S 20 20 30 30") and ' +
+                'path("M 0 0 S 40 40 0 0")');
+}, 'The smooth cubic Bézier curve commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 0 0 Q 10 10 30 30")',
+                         'path("M 0 0 Q 20 20 0 0")');
+  assert_equals(dist,
+                Math.sqrt(10 * 10 * 2 + 30 * 30 * 2),
+                'path("M 0 0 Q 10 10 30 30") and ' +
+                'path("M 0 0 Q 20 20 0 0")');
+}, 'The quadratic cubic Bézier curve commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 0 0 T 30 30")',
+                         'path("M 0 0 T 0 0")');
+  assert_equals(dist,
+                Math.sqrt(30 * 30 * 2),
+                'path("M 0 0 T 30 30") and ' +
+                'path("M 0 0 T 0 0")');
+}, 'The smooth quadratic cubic Bézier curve commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("M 0 0 A 5 5 10 0 1 30 30")',
+                         'path("M 0 0 A 4 4 5 0 0 20 20")');
+  assert_equals(dist,
+                Math.sqrt(1 * 1 * 2 + // radii
+                          5 * 5 +     // angle
+                          1 * 1 +     // flag
+                          10 * 10 * 2),
+                'path("M 0 0 A 5 5 10 0 1 30 30") and ' +
+                'path("M 0 0 A 4 4 5 0 0 20 20")');
+}, 'The elliptical arc curve commands');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'offset-path',
+                         'path("m 10 20 h 30 v 60 h 10 v -10 l 110 60")',
+                   // == 'path("M  10  20 H  40 V  80 H  50 V  70 L 160 130")'
+                         'path("M 130 140 H 120 V 160 H 130 V 150 L 200 170")');
+  assert_equals(dist,
+                Math.sqrt(120 * 120 * 2 +
+                          80 * 80 * 4 +
+                          40 * 40 * 2),
+                'path("m 10 20 h 30 v 60 h 10 v -10 l 110 60") and ' +
+                'path("M 130 140 H 120 V 160 H 130 V 150 L 200 170")');
+}, 'The distance of paths with absolute and relative coordinates');
+
+</script>
+</html>
diff --git a/dom/animation/test/mozilla/test_distance_of_transform.html b/dom/animation/test/mozilla/test_distance_of_transform.html
new file mode 100644
index 0000000000..96ff1eb66d
--- /dev/null
+++ b/dom/animation/test/mozilla/test_distance_of_transform.html
@@ -0,0 +1,404 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src='/resources/testharness.js'></script>
+<script src='/resources/testharnessreport.js'></script>
+<script src='../testcommon.js'></script>
+<div id='log'></div>
+<script type='text/javascript'>
+'use strict';
+
+// We don't have an official spec to define the distance between two transform
+// lists, but we still need this for DevTools, so Gecko and Servo backend use
+// the similar rules to define the distance. If there is a spec for it, we have
+// to update this test file.
+
+const EPSILON = 0.00001;
+
+// |v| should be a unit vector (i.e. having length 1)
+function getQuaternion(v, angle) {
+  return [
+    v[0] * Math.sin(angle / 2.0),
+    v[1] * Math.sin(angle / 2.0),
+    v[2] * Math.sin(angle / 2.0),
+    Math.cos(angle / 2.0)
+  ];
+}
+
+function computeRotateDistance(q1, q2) {
+  const dot = q1.reduce((sum, e, i) => sum + e * q2[i], 0);
+  return Math.acos(Math.min(Math.max(dot, -1.0), 1.0)) * 2.0;
+}
+
+function createMatrixFromArray(array) {
+  return (array.length === 16 ? 'matrix3d' : 'matrix') + `(${array.join()})`;
+}
+
+function rotate3dToMatrix(x, y, z, radian) {
+  var sc = Math.sin(radian / 2) * Math.cos(radian / 2);
+  var sq = Math.sin(radian / 2) * Math.sin(radian / 2);
+
+  // Normalize the vector.
+  var length = Math.sqrt(x*x + y*y + z*z);
+  x /= length;
+  y /= length;
+  z /= length;
+
+  return [
+    1 - 2 * (y*y + z*z) * sq,
+    2 * (x * y * sq + z * sc),
+    2 * (x * z * sq - y * sc),
+    0,
+    2 * (x * y * sq - z * sc),
+    1 - 2 * (x*x + z*z) * sq,
+    2 * (y * z * sq + x * sc),
+    0,
+    2 * (x * z * sq + y * sc),
+    2 * (y * z * sq - x * sc),
+    1 - 2 * (x*x + y*y) * sq,
+    0,
+    0,
+    0,
+    0,
+    1
+  ];
+}
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform', 'none', 'none');
+  assert_equals(dist, 0, 'distance of translate');
+}, 'Test distance of none and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform', 'translate(100px)', 'none');
+  assert_equals(dist, 100, 'distance of translate');
+}, 'Test distance of translate function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist =
+    getDistance(target, 'transform', 'translate(100px)', 'translate(200px)');
+  assert_equals(dist, 200 - 100, 'distance of translate');
+}, 'Test distance of translate functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist =
+    getDistance(target, 'transform', 'translate3d(100px, 0, 50px)', 'none');
+  assert_equals(dist, Math.sqrt(100 * 100 + 50 * 50),
+                'distance of translate3d');
+}, 'Test distance of translate3d function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist =
+    getDistance(target, 'transform',
+                'translate3d(100px, 0, 50px)',
+                'translate3d(200px, 80px, 0)');
+  assert_equals(dist, Math.sqrt(100 * 100 + 80 * 80 + 50 * 50),
+                'distance of translate');
+}, 'Test distance of translate3d functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform', 'scale(1.5)', 'none');
+  assert_equals(dist, Math.sqrt(0.5 * 0.5 + 0.5 * 0.5), 'distance of scale');
+}, 'Test distance of scale function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform', 'scale(1.5)', 'scale(2.0)');
+  assert_equals(dist, Math.sqrt(0.5 * 0.5 + 0.5 * 0.5), 'distance of scale');
+}, 'Test distance of scale functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'scale3d(1.5, 1.5, 1.5)',
+                         'none');
+  assert_equals(dist,
+                Math.sqrt(0.5 * 0.5 + 0.5 * 0.5 + 0.5 * 0.5),
+                'distance of scale3d');
+}, 'Test distance of scale3d function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'scale3d(1.5, 1.5, 1.5)',
+                         'scale3d(2.0, 2.0, 1.0)');
+  assert_equals(dist,
+                Math.sqrt(0.5 * 0.5 + 0.5 * 0.5 + 0.5 * 0.5),
+                'distance of scale3d');
+}, 'Test distance of scale3d functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist =
+    getDistance(target, 'transform', 'rotate(45deg)', 'rotate(90deg)');
+  assert_approx_equals(dist, Math.PI / 2.0 - Math.PI / 4.0, EPSILON, 'distance of rotate');
+}, 'Test distance of rotate functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist =
+    getDistance(target, 'transform', 'rotate(45deg)', 'none');
+  assert_approx_equals(dist, Math.PI / 4.0, EPSILON, 'distance of rotate');
+}, 'Test distance of rotate function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'rotate3d(0, 1, 0, 90deg)',
+                         'none');
+  assert_approx_equals(dist, Math.PI / 2, EPSILON, 'distance of rotate3d');
+}, 'Test distance of rotate3d function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'rotate3d(0, 0, 1, 90deg)',
+                         'rotate3d(1, 0, 0, 90deg)');
+  let q1 = getQuaternion([0, 0, 1], Math.PI / 2.0);
+  let q2 = getQuaternion([1, 0, 0], Math.PI / 2.0);
+  assert_approx_equals(dist, computeRotateDistance(q1, q2), EPSILON, 'distance of rotate3d');
+}, 'Test distance of rotate3d functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'rotate3d(0, 0, 1, 90deg)',
+                         'rotate3d(0, 0, 0, 90deg)');
+  assert_approx_equals(dist, Math.PI / 2, EPSILON, 'distance of rotate3d');
+}, 'Test distance of rotate3d functions whose direction vector cannot be ' +
+   'normalized');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform', 'skew(1rad, 0.5rad)', 'none');
+  assert_approx_equals(dist, Math.sqrt(1 * 1 + 0.5 * 0.5), EPSILON, 'distance of skew');
+}, 'Test distance of skew function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'skew(1rad, 0.5rad)',
+                         'skew(-1rad, 0)');
+  assert_approx_equals(dist, Math.sqrt(2 * 2 + 0.5 * 0.5), EPSILON, 'distance of skew');
+}, 'Test distance of skew functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'perspective(128px)',
+                         'none');
+  assert_equals(dist, Infinity, 'distance of perspective');
+}, 'Test distance of perspective function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  // perspective(0) is treated as perspective(inf) because perspective length
+  // should be greater than or equal to zero.
+  var dist = getDistance(target, 'transform',
+                         'perspective(128px)',
+                         'perspective(0)');
+  assert_equals(dist, 128, 'distance of perspective');
+}, 'Test distance of perspective function and an invalid perspective');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'perspective(128px)',
+                         'perspective(1024px)');
+  assert_equals(dist, 1024 - 128, 'distance of perspective');
+}, 'Test distance of perspective functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var sin_30 = Math.sin(Math.PI / 6);
+  var cos_30 = Math.cos(Math.PI / 6);
+  // matrix => translate(100, 0) rotate(30deg).
+  var matrix = createMatrixFromArray([ cos_30, sin_30,
+                                      -sin_30, cos_30,
+                                       100, 0 ]);
+  var dist = getDistance(target, 'transform', matrix, 'none');
+  assert_approx_equals(dist,
+                       Math.sqrt(100 * 100 + (Math.PI / 6) * (Math.PI / 6)),
+                       EPSILON,
+                       'distance of matrix');
+}, 'Test distance of matrix function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var sin_30 = Math.sin(Math.PI / 6);
+  var cos_30 = Math.cos(Math.PI / 6);
+  // matrix1 => translate(100, 0) rotate(30deg).
+  var matrix1 = createMatrixFromArray([ cos_30, sin_30,
+                                       -sin_30, cos_30,
+                                        100, 0 ]);
+  // matrix2 => translate(0, 100) scale(0.5).
+  var matrix2 = createMatrixFromArray([ 0.5, 0, 0, 0.5, 0, 100 ]);
+  var dist = getDistance(target, 'transform', matrix1, matrix2);
+  assert_approx_equals(dist,
+                       Math.sqrt(100 * 100 + 100 * 100 +          // translate
+                                 (Math.PI / 6) * (Math.PI / 6) +  // rotate
+                                 0.5 * 0.5 + 0.5 * 0.5),          // scale
+                       EPSILON,
+                       'distance of matrix');
+}, 'Test distance of matrix functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var matrix = createMatrixFromArray(rotate3dToMatrix(0, 1, 0, Math.PI / 6));
+  var dist = getDistance(target, 'transform', matrix, 'none');
+  assert_approx_equals(dist, Math.PI / 6, EPSILON, 'distance of matrix3d');
+}, 'Test distance of matrix3d function and none');
+
+test(function(t) {
+  var target = addDiv(t);
+  // matrix1 => rotate3d(0, 1, 0, 30deg).
+  var matrix1 = createMatrixFromArray(rotate3dToMatrix(0, 1, 0, Math.PI / 6));
+  // matrix1 => translate3d(100, 0, 0) scale3d(0.5, 0.5, 0.5).
+  var matrix2 = createMatrixFromArray([ 0.5, 0, 0, 0,
+                                        0, 0.5, 0, 0,
+                                        0, 0, 0.5, 0,
+                                        100, 0, 0, 1 ]);
+  var dist = getDistance(target, 'transform', matrix1, matrix2);
+  assert_approx_equals(dist,
+                       Math.sqrt(100 * 100 +                      // translate
+                                 0.5 * 0.5 * 3 +                  // scale
+                                 (Math.PI / 6) * (Math.PI / 6)),  // rotate
+                       EPSILON,
+                       'distance of matrix');
+}, 'Test distance of matrix3d functions');
+
+test(function(t) {
+  var target = addDiv(t);
+  var cos_180 = Math.cos(Math.PI);
+  var sin_180 = Math.sin(Math.PI);
+  // matrix1 => translate3d(100px, 50px, -10px) skew(45deg).
+  var matrix1 = createMatrixFromArray([ 1, 0, 0, 0,
+                                        Math.tan(Math.PI/4.0), 1, 0, 0,
+                                        0, 0, 1, 0,
+                                        100, 50, -10, 1]);
+  // matrix2 => translate3d(1000px, 0, 0) rotate3d(1, 0, 0, 180deg).
+  var matrix2 = createMatrixFromArray([ 1, 0, 0, 0,
+                                        0, cos_180, sin_180, 0,
+                                        0, -sin_180, cos_180, 0,
+                                        1000, 0, 0, 1 ]);
+  var dist = getDistance(target, 'transform', matrix1, matrix2);
+  assert_approx_equals(dist,
+                       Math.sqrt(900 * 900 + 50 * 50 + 10 * 10 +  // translate
+                                 Math.PI * Math.PI +              // rotate
+                                 (Math.PI / 4) * (Math.PI / 4)),  // skew angle
+                       EPSILON,
+                       'distance of matrix');
+}, 'Test distance of matrix3d functions with skew factors');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist =
+    getDistance(target, 'transform',
+                'rotate(180deg) translate(1000px)',
+                'rotate(360deg) translate(0px)');
+  assert_approx_equals(dist, Math.sqrt(1000 * 1000 + Math.PI * Math.PI), EPSILON,
+                       'distance of transform lists');
+}, 'Test distance of transform lists');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'translate(100px) rotate(180deg)',
+                         'translate(50px) rotate(90deg) scale(5) skew(1rad)');
+  assert_approx_equals(dist,
+                       Math.sqrt(50 * 50 +
+                                 Math.PI / 2 * Math.PI / 2 +
+                                 4 * 4 * 2 +
+                                 1 * 1),
+                       EPSILON,
+                       'distance of transform lists');
+}, 'Test distance of transform lists where one has extra items');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'translate(1000px) rotate3d(1, 0, 0, 180deg)',
+                         'translate(1000px) scale3d(2.5, 0.5, 1)');
+  assert_equals(dist, Math.sqrt(Math.PI * Math.PI + 1.5 * 1.5 + 0.5 * 0.5),
+                'distance of transform lists');
+}, 'Test distance of mismatched transform lists');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'transform',
+                         'translate(100px) skew(1rad)',
+                         'translate(1000px) rotate3d(0, 1, 0, -2rad)');
+  assert_approx_equals(dist,
+                       Math.sqrt(900 * 900 + 1 * 1 + 2 * 2),
+                       EPSILON,
+                       'distance of transform lists');
+}, 'Test distance of mismatched transform lists with skew function');
+
+
+// Individual transforms
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'translate', '50px', 'none');
+  assert_equals(dist, Math.sqrt(50 * 50), 'distance of 2D translate and none');
+}, 'Test distance of 2D translate property with none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'translate', '10px 30px', '50px');
+  assert_equals(dist, Math.sqrt(40 * 40 + 30 * 30), 'distance of 2D translate');
+}, 'Test distance of 2D translate property');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'translate', '10px 30px 50px', '50px');
+  assert_equals(dist, Math.sqrt(40 * 40 + 30 * 30 + 50 * 50),
+                'distance of 3D translate');
+}, 'Test distance of 3D translate property');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'scale', '2', 'none');
+  assert_equals(dist, Math.sqrt(1 + 1), 'distance of 2D scale and none');
+}, 'Test distance of 2D scale property with none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'scale', '3', '1 1');
+  assert_equals(dist, Math.sqrt(2 * 2 + 2 * 2), 'distance of 2D scale');
+}, 'Test distance of 2D scale property');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'scale', '3 2 2', '1 1');
+  assert_equals(dist, Math.sqrt(2 * 2 + 1 * 1 + 1 * 1),
+                'distance of 3D scale');
+}, 'Test distance of 3D scale property');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'rotate', '180deg', 'none');
+  assert_equals(dist, Math.PI, 'distance of 2D rotate and none');
+}, 'Test distance of 2D rotate property with none');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'rotate', '180deg', '90deg');
+  assert_equals(dist, Math.PI / 2.0, 'distance of 2D rotate');
+}, 'Test distance of 2D rotate property');
+
+test(function(t) {
+  var target = addDiv(t);
+  var dist = getDistance(target, 'rotate', 'z 90deg', 'x 90deg');
+  let q1 = getQuaternion([0, 0, 1], Math.PI / 2.0);
+  let q2 = getQuaternion([1, 0, 0], Math.PI / 2.0);
+  assert_approx_equals(dist, computeRotateDistance(q1, q2), EPSILON,
+                       'distance of 3D rotate');
+}, 'Test distance of 3D rotate property');
+
+</script>
+</html>
diff --git a/dom/animation/test/mozilla/test_document_timeline_origin_time_range.html b/dom/animation/test/mozilla/test_document_timeline_origin_time_range.html
new file mode 100644
index 0000000000..b2aeef8a77
--- /dev/null
+++ b/dom/animation/test/mozilla/test_document_timeline_origin_time_range.html
@@ -0,0 +1,32 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+// If the originTime parameter passed to the DocumentTimeline exceeds
+// the range of the internal storage type (a signed 64-bit integer number
+// of ticks--a platform-dependent unit) then we should throw.
+// Infinity isn't allowed as an origin time value and clamping to just
+// inside the allowed range will just mean we overflow elsewhere.
+
+test(function(t) {
+  assert_throws({ name: 'TypeError'},
+    function() {
+      new DocumentTimeline({ originTime: Number.MAX_SAFE_INTEGER });
+    });
+}, 'Calculated current time is positive infinity');
+
+test(function(t) {
+  assert_throws({ name: 'TypeError'},
+    function() {
+      new DocumentTimeline({ originTime: -1 * Number.MAX_SAFE_INTEGER });
+    });
+}, 'Calculated current time is negative infinity');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_event_listener_leaks.html b/dom/animation/test/mozilla/test_event_listener_leaks.html
new file mode 100644
index 0000000000..bcfadaf9e9
--- /dev/null
+++ b/dom/animation/test/mozilla/test_event_listener_leaks.html
@@ -0,0 +1,43 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Bug 1450271 - Test Animation event listener leak conditions</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/dom/events/test/event_leak_utils.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script class="testbody" type="text/javascript">
+// Manipulate Animation.  Its important here that we create a
+// listener callback from the DOM objects back to the frame's global
+// in order to exercise the leak condition.
+async function useAnimation(contentWindow) {
+  let div = contentWindow.document.createElement("div");
+  contentWindow.document.body.appendChild(div);
+  let animation = div.animate({}, 100 * 1000);
+  is(animation.playState, "running", "animation should be running");
+  animation.onfinish = _ => {
+    contentWindow.finishCount += 1;
+  };
+}
+
+async function runTest() {
+  try {
+    await checkForEventListenerLeaks("Animation", useAnimation);
+  } catch (e) {
+    ok(false, e);
+  } finally {
+    SimpleTest.finish();
+  }
+}
+
+SimpleTest.waitForExplicitFinish();
+addEventListener("load", runTest, { once: true });
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/animation/test/mozilla/test_get_animations_on_scroll_animations.html b/dom/animation/test/mozilla/test_get_animations_on_scroll_animations.html
new file mode 100644
index 0000000000..7d20e5b70b
--- /dev/null
+++ b/dom/animation/test/mozilla/test_get_animations_on_scroll_animations.html
@@ -0,0 +1,74 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Test getAnimations() which doesn't return scroll animations</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<style>
+  @keyframes animWidth {
+    from { width: 100px; }
+    to { width: 200px }
+  }
+  @keyframes animTop {
+    to { top: 100px }
+  }
+  .fill-vh {
+    width: 100px;
+    height: 100vh;
+  }
+</style>
+</head>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+test(function(t) {
+  const div = addDiv(t,
+    { style: "width: 10px; height: 100px; " +
+             "animation: animWidth 100s scroll(), animTop 200s;" });
+
+  // Sanity check to make sure the scroll animation is there.
+  addDiv(t, { class: "fill-vh" });
+  const scroller = document.scrollingElement;
+  const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+  scroller.scrollTop = maxScroll;
+  assert_equals(getComputedStyle(div).width, "200px",
+                "The scroll animation is there");
+
+  const animations = div.getAnimations();
+  assert_equals(animations.length, 2,
+                'getAnimations() should include scroll animations');
+  assert_equals(animations[0].animationName, "animWidth",
+                'getAmimations() should return scroll animations');
+  // FIXME: Bug 1676794. Support ScrollTimeline interface.
+  assert_equals(animations[0].timeline, null,
+                'scroll animation should not return scroll timeline');
+}, 'Element.getAnimation() should include scroll animations');
+
+test(function(t) {
+  const div = addDiv(t,
+    { style: "width: 10px; height: 100px; " +
+             "animation: animWidth 100s scroll(), animTop 100s;" });
+
+  // Sanity check to make sure the scroll animation is there.
+  addDiv(t, { class: "fill-vh" });
+  const scroller = document.scrollingElement;
+  const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+  scroller.scrollTop = maxScroll;
+  assert_equals(getComputedStyle(div).width, "200px",
+                "The scroll animation is there");
+
+  const animations = document.getAnimations();
+  assert_equals(animations.length, 2,
+                'getAnimations() should include scroll animations');
+  assert_equals(animations[0].animationName, "animWidth",
+                'getAmimations() should return scroll animations');
+  // FIXME: Bug 1676794. Support ScrollTimeline interface.
+  assert_equals(animations[0].timeline, null,
+                'scroll animation should not return scroll timeline');
+}, 'Document.getAnimation() should include scroll animations');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_hide_and_show.html b/dom/animation/test/mozilla/test_hide_and_show.html
new file mode 100644
index 0000000000..f36543bb1e
--- /dev/null
+++ b/dom/animation/test/mozilla/test_hide_and_show.html
@@ -0,0 +1,198 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<style>
+@keyframes move {
+  100% {
+    transform: translateX(100px);
+  }
+}
+
+div.pseudo::before {
+  animation: move 0.01s;
+  content: 'content';
+}
+
+</style>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+test(function(t) {
+  var div = addDiv(t, { style: 'animation: move 100s infinite' });
+  assert_equals(div.getAnimations().length, 1,
+                'display:initial element has animations');
+
+  div.style.display = 'none';
+  assert_equals(div.getAnimations().length, 0,
+                'display:none element has no animations');
+}, 'Animation stops playing when the element style display is set to "none"');
+
+test(function(t) {
+  var parentElement = addDiv(t);
+  var div = addDiv(t, { style: 'animation: move 100s infinite' });
+  parentElement.appendChild(div);
+  assert_equals(div.getAnimations().length, 1,
+                'display:initial element has animations');
+
+  parentElement.style.display = 'none';
+  assert_equals(div.getAnimations().length, 0,
+                'Element in display:none subtree has no animations');
+}, 'Animation stops playing when its parent element style display is set ' +
+   'to "none"');
+
+test(function(t) {
+  var div = addDiv(t, { style: 'animation: move 100s infinite' });
+  assert_equals(div.getAnimations().length, 1,
+                'display:initial element has animations');
+
+  div.style.display = 'none';
+  assert_equals(div.getAnimations().length, 0,
+                'display:none element has no animations');
+
+  div.style.display = '';
+  assert_equals(div.getAnimations().length, 1,
+                'Element which is no longer display:none has animations ' +
+                'again');
+}, 'Animation starts playing when the element gets shown from ' +
+   '"display:none" state');
+
+test(function(t) {
+  var parentElement = addDiv(t);
+  var div = addDiv(t, { style: 'animation: move 100s infinite' });
+  parentElement.appendChild(div);
+  assert_equals(div.getAnimations().length, 1,
+                'display:initial element has animations');
+
+  parentElement.style.display = 'none';
+  assert_equals(div.getAnimations().length, 0,
+                'Element in display:none subtree has no animations');
+
+  parentElement.style.display = '';
+  assert_equals(div.getAnimations().length, 1,
+                'Element which is no longer in display:none subtree has ' +
+                'animations again');
+}, 'Animation starts playing when its parent element is shown from ' +
+   '"display:none" state');
+
+test(function(t) {
+  var div = addDiv(t, { style: 'animation: move 100s forwards' });
+  assert_equals(div.getAnimations().length, 1,
+                'display:initial element has animations');
+
+  var animation = div.getAnimations()[0];
+  animation.finish();
+  assert_equals(div.getAnimations().length, 1,
+                'Element has finished animation if the animation ' +
+                'fill-mode is forwards');
+
+  div.style.display = 'none';
+  assert_equals(animation.playState, 'idle',
+                'The animation.playState should be idle');
+
+  assert_equals(div.getAnimations().length, 0,
+                'display:none element has no animations');
+
+  div.style.display = '';
+  assert_equals(div.getAnimations().length, 1,
+                'Element which is no longer display:none has animations ' +
+                'again');
+  assert_not_equals(div.getAnimations()[0], animation,
+                    'Restarted animation is a newly-generated animation');
+
+}, 'Animation which has already finished starts playing when the element ' +
+   'gets shown from "display:none" state');
+
+test(function(t) {
+  var parentElement = addDiv(t);
+  var div = addDiv(t, { style: 'animation: move 100s forwards' });
+  parentElement.appendChild(div);
+  assert_equals(div.getAnimations().length, 1,
+                'display:initial element has animations');
+
+  var animation = div.getAnimations()[0];
+  animation.finish();
+  assert_equals(div.getAnimations().length, 1,
+                'Element has finished animation if the animation ' +
+                'fill-mode is forwards');
+
+  parentElement.style.display = 'none';
+  assert_equals(animation.playState, 'idle',
+                'The animation.playState should be idle');
+  assert_equals(div.getAnimations().length, 0,
+                'Element in display:none subtree has no animations');
+
+  parentElement.style.display = '';
+  assert_equals(div.getAnimations().length, 1,
+                'Element which is no longer in display:none subtree has ' +
+                'animations again');
+
+  assert_not_equals(div.getAnimations()[0], animation,
+                    'Restarted animation is a newly-generated animation');
+
+}, 'Animation with fill:forwards which has already finished starts playing ' +
+   'when its parent element is shown from "display:none" state');
+
+test(function(t) {
+  var parentElement = addDiv(t);
+  var div = addDiv(t, { style: 'animation: move 100s' });
+  parentElement.appendChild(div);
+  assert_equals(div.getAnimations().length, 1,
+                'display:initial element has animations');
+
+  var animation = div.getAnimations()[0];
+  animation.finish();
+  assert_equals(div.getAnimations().length, 0,
+                'Element does not have finished animations');
+
+  parentElement.style.display = 'none';
+  assert_equals(animation.playState, 'idle',
+                'The animation.playState should be idle');
+  assert_equals(div.getAnimations().length, 0,
+                'Element in display:none subtree has no animations');
+
+  parentElement.style.display = '';
+  assert_equals(div.getAnimations().length, 1,
+                'Element which is no longer in display:none subtree has ' +
+                'animations again');
+
+  assert_not_equals(div.getAnimations()[0], animation,
+                    'Restarted animation is a newly-generated animation');
+
+}, 'CSS Animation which has already finished starts playing when its parent ' +
+   'element is shown from "display:none" state');
+
+promise_test(function(t) {
+  var div = addDiv(t, { 'class': 'pseudo' });
+  var eventWatcher = new EventWatcher(t, div, 'animationend');
+
+  assert_equals(document.getAnimations().length, 1,
+                'CSS animation on pseudo element');
+
+  return eventWatcher.wait_for('animationend').then(function() {
+    assert_equals(document.getAnimations().length, 0,
+                  'No CSS animation on pseudo element after the animation ' +
+                  'finished');
+
+    // Remove the class which generated this pseudo element.
+    div.classList.remove('pseudo');
+
+    // We need to wait for two frames to process re-framing.
+    // The callback of 'animationend' is processed just before rAF callbacks,
+    // and rAF callbacks are processed before re-framing process, so waiting for
+    // one rAF callback is not sufficient.
+    return waitForAnimationFrames(2);
+  }).then(function() {
+    // Add the class again to re-generate pseudo element.
+    div.classList.add('pseudo');
+    assert_equals(document.getAnimations().length, 1,
+                  'A new CSS animation on pseudo element');
+  });
+}, 'CSS animation on pseudo element restarts after the pseudo element that ' +
+   'had a finished CSS animation is re-generated');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_mainthread_synchronization_pref.html b/dom/animation/test/mozilla/test_mainthread_synchronization_pref.html
new file mode 100644
index 0000000000..3653fd9536
--- /dev/null
+++ b/dom/animation/test/mozilla/test_mainthread_synchronization_pref.html
@@ -0,0 +1,42 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<style>
+.compositable {
+  /* Element needs geometry to be eligible for layerization */
+  width: 100px;
+  height: 100px;
+  background-color: white;
+}
+</style>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+promise_test(async t => {
+  await SpecialPowers.pushPrefEnv({
+    set: [[ 'dom.animations.mainthread-synchronization-with-geometric-animations', false ]]
+  });
+
+  const elemA = addDiv(t, { class: 'compositable' });
+  const elemB = addDiv(t, { class: 'compositable' });
+
+  const animA = elemA.animate({ transform: [ 'translate(0px)',
+                                             'translate(100px)' ] },
+                              100 * MS_PER_SEC);
+  const animB = elemB.animate({ marginLeft: [ '0px', '100px' ] },
+                              100 * MS_PER_SEC);
+
+  await waitForPaints();
+
+  assert_true(SpecialPowers.wrap(animA).isRunningOnCompositor,
+      'Transform animation should not synchronize with margin-left animation ' +
+      'created within the same tick with disabling the corresponding pref');
+}, 'Transform animation should not synchronize with margin-left animation '
+   + 'created within the same tick with disabling the corresponding pref');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_moz_prefixed_properties.html b/dom/animation/test/mozilla/test_moz_prefixed_properties.html
new file mode 100644
index 0000000000..f65d05134d
--- /dev/null
+++ b/dom/animation/test/mozilla/test_moz_prefixed_properties.html
@@ -0,0 +1,93 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test animations of all properties that have -moz prefix</title>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <script src="../testcommon.js"></script>
+  <script src="../property_database.js"></script>
+</head>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+const testcases = [
+  {
+    property: "-moz-box-align"
+  },
+  {
+    property: "-moz-box-direction"
+  },
+  {
+    property: "-moz-box-ordinal-group"
+  },
+  {
+    property: "-moz-box-orient",
+  },
+  {
+    property: "-moz-box-pack"
+  },
+  {
+    property: "-moz-float-edge"
+  },
+  {
+    property: "-moz-force-broken-image-icon"
+  },
+  {
+    property: "-moz-orient"
+  },
+  {
+    property: "-moz-osx-font-smoothing",
+    pref: "layout.css.osx-font-smoothing.enabled"
+  },
+  {
+    property: "-moz-text-size-adjust"
+  },
+  {
+    property: "-moz-user-focus"
+  },
+  {
+    property: "-moz-user-input"
+  },
+  {
+    property: "-moz-user-modify"
+  },
+  {
+    property: "user-select"
+  },
+  {
+    property: "-moz-window-dragging"
+  },
+];
+
+testcases.forEach(testcase => {
+  if (testcase.pref && !IsCSSPropertyPrefEnabled(testcase.pref)) {
+    return;
+  }
+
+  const property = gCSSProperties[testcase.property];
+  const values = property.initial_values.concat(property.other_values);
+  values.forEach(value => {
+    test(function(t) {
+      const container = addDiv(t);
+      const target = document.createElement("div");
+      container.appendChild(target);
+
+      container.style[property.domProp] = value;
+
+      const animation =
+        target.animate({ [property.domProp]: [value, "inherit"] },
+                       { duration: 1000, delay: -500 } );
+
+      const expectedValue = getComputedStyle(container)[property.domProp];
+      assert_equals(getComputedStyle(target)[property.domProp], expectedValue,
+                    `Computed style shoud be "${ expectedValue }"`);
+    }, `Test inherit value for "${ testcase.property }" `
+       + `(Parent element style is "${ value }")`);
+  });
+});
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/animation/test/mozilla/test_pending_animation_tracker.html b/dom/animation/test/mozilla/test_pending_animation_tracker.html
new file mode 100644
index 0000000000..022efa7bcf
--- /dev/null
+++ b/dom/animation/test/mozilla/test_pending_animation_tracker.html
@@ -0,0 +1,134 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Test animations in PendingAnimationTracker</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+</head>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+promise_test(function waitForLoad() {
+  return new Promise(resolve => {
+    window.addEventListener("load", resolve, { once: true });
+  });
+});
+
+promise_test(async t => {
+  // See below, but we should ensure we are in a rAF callback before proceeding
+  // or else we will get inconsistent results.
+  await waitForNextFrame();
+
+  const target = addDiv(t);
+  const anim = target.animate(null, 100 * MS_PER_SEC);
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be tracked by tracker');
+
+  anim.effect = null;
+  await waitForNextFrame();
+
+  assert_false(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+               'The animation should NOT be tracked by the tracker');
+}, 'An animation whose effect is made null while pending is subsequently'
+   + ' removed from the tracker');
+
+test(t => {
+  const target = addDiv(t);
+  const anim = target.animate(null, 100 * MS_PER_SEC);
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be tracked by tracker');
+
+  const newEffect = new KeyframeEffect(target, null);
+  anim.effect = newEffect;
+
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be still tracked by tracker');
+}, 'Setting another effect keeps the pending animation in the tracker');
+
+test(t => {
+  const effect = new KeyframeEffect(null, null);
+  const anim = new Animation(effect);
+  anim.play();
+  assert_false(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+               'The orphaned animation should NOT be tracked by tracker');
+
+  const target = addDiv(t);
+  const newEffect = new KeyframeEffect(target, null);
+  anim.effect = newEffect;
+
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be now tracked by tracker');
+}, 'Setting effect having target element starts being tracked by the ' +
+   'tracker');
+
+test(t => {
+  const target = addDiv(t);
+  const anim = target.animate(null, 100 * MS_PER_SEC);
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be tracked by tracker');
+
+  anim.cancel();
+
+  assert_false(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+               'The animation should NOT be tracked by the tracker');
+}, 'Calling cancel() removes the animation from the tracker');
+
+promise_test(async t => {
+  // Before proceeding this test, make sure following code is _NOT_ processed
+  // between paint and refresh driver's tick.  Otherwise, waitForNextFrame below
+  // doesn't ensure that a paint process happens which means that there is
+  // no chance to call TriggerPendingAnimationsOnNextTick to discard the
+  // animation from the pending animation tracker.
+  await waitForNextFrame();
+
+  const target = addDiv(t);
+  const anim = target.animate(null, 100 * MS_PER_SEC);
+
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be tracked by tracker');
+
+  target.remove();
+
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation is still being tracked by the tracker');
+
+  await waitForNextFrame();
+  assert_false(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+               'The animation should NOT be tracked by the tracker in the ' +
+               'next frame');
+}, 'Removing target element from the document removes the animation from ' +
+   'the tracker in the next tick');
+
+test(t => {
+  const target = addDiv(t);
+  const anotherTarget = addDiv(t);
+  const anim = target.animate(null, 100 * MS_PER_SEC);
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be tracked by tracker');
+
+  anim.effect.target = anotherTarget;
+
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be still tracked by tracker');
+}, 'Setting another target keeps the pending animation in the tracker');
+
+test(t => {
+  const effect = new KeyframeEffect(null, null);
+  const anim = new Animation(effect);
+  anim.play();
+  assert_false(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+               'The orphaned animation should NOT be tracked by tracker');
+
+  const target = addDiv(t);
+  anim.effect.target = target;
+
+  assert_true(SpecialPowers.DOMWindowUtils.isAnimationInPendingTracker(anim),
+              'The animation should be now tracked by tracker');
+}, 'Setting target element to the orphaned animation starts being tracked ' +
+   'by the tracker');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_restyles.html b/dom/animation/test/mozilla/test_restyles.html
new file mode 100644
index 0000000000..bc1ab70c74
--- /dev/null
+++ b/dom/animation/test/mozilla/test_restyles.html
@@ -0,0 +1,22 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+<div id='log'></div>
+<script>
+'use strict';
+SimpleTest.waitForExplicitFinish();
+SimpleTest.expectAssertions(0, 1); // bug 1332970
+SpecialPowers.pushPrefEnv(
+  {
+    set: [
+      ['layout.reflow.synthMouseMove', false],
+      ['privacy.reduceTimerPrecision', false],
+    ],
+  },
+  function() {
+    window.open('file_restyles.html');
+  }
+);
+</script>
+</html>
diff --git a/dom/animation/test/mozilla/test_restyling_xhr_doc.html b/dom/animation/test/mozilla/test_restyling_xhr_doc.html
new file mode 100644
index 0000000000..67b6ac8845
--- /dev/null
+++ b/dom/animation/test/mozilla/test_restyling_xhr_doc.html
@@ -0,0 +1,106 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="../testcommon.js"></script>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+
+// This test supplements the web-platform-tests in:
+//
+//   web-animations/interfaces/Animatable/animate-no-browsing-context.html
+//
+// Specifically, it covers the case where we have a running animation
+// targetting an element in a document without a browsing context.
+//
+// Currently the behavior in this case is not well-defined. For example,
+// if we were to simply take an element from such a document, and do:
+//
+//  const xdoc = xhr.responseXML;
+//  const div = xdoc.getElementById('test');
+//  div.style.opacity = '0';
+//  alert(getComputedStyle(div).opacity);
+//
+// We'd get '0' in Firefox and Edge, but an empty string in Chrome.
+//
+// However, if instead of using the style attribute, we set style in a <style>
+// element in *either* the document we're calling from *or* the XHR doc and
+// do the same we get '1' in Firefox and Edge, but an empty string in Chrome.
+//
+// That is, no browser appears to apply styles to elements in a document without
+// a browsing context unless the styles are defined using the style attribute,
+// and even then Chrome does not.
+//
+// There is some prose in CSSOM which says,
+//
+//    Note: This means that even if obj is in a different document (e.g. one
+//    fetched via XMLHttpRequest) it will still use the style rules associated
+//    with the document that is associated with the global object on which
+//    getComputedStyle() was invoked to compute the CSS declaration block.[1]
+//
+// However, this text has been around since at least 2013 and does not appear
+// to be implemented.
+//
+// As a result, it's not really possible to write a cross-browser test for the
+// behavior for animations in this context since it's not clear what the result
+// should be. That said, we still want to exercise this particular code path so
+// we make this case a Mozilla-specific test. The other similar tests cases for
+// which the behavior is well-defined are covered by web-platform-tests.
+//
+// [1] https://drafts.csswg.org/cssom/#extensions-to-the-window-interface
+
+function getXHRDoc(t) {
+  return new Promise(resolve => {
+    const xhr = new XMLHttpRequest();
+    xhr.open('GET', 'xhr_doc.html');
+    xhr.responseType = 'document';
+    xhr.onload = t.step_func(() => {
+      assert_equals(xhr.readyState, xhr.DONE,
+                    'Request should complete successfully');
+      assert_equals(xhr.status, 200,
+                    'Response should be OK');
+      resolve(xhr.responseXML);
+    });
+    xhr.send();
+  });
+}
+
+promise_test(t => {
+  let anim;
+  return getXHRDoc(t).then(xhrdoc => {
+    const div = xhrdoc.getElementById('test');
+    anim = div.animate({ opacity: [ 0, 1 ] }, 1000);
+    // Give the animation an active timeline and kick-start it.
+    anim.timeline = document.timeline;
+    anim.startTime = document.timeline.currentTime;
+    assert_equals(anim.playState, 'running',
+                  'The animation should be running');
+    // Gecko currently skips applying animation styles to elements in documents
+    // without browsing contexts.
+    assert_not_equals(getComputedStyle(div).opacity, '0',
+                      'Style should NOT be updated');
+  });
+}, 'Forcing an animation targetting an element in a document without a'
+    + ' browsing context to play does not cause style to update');
+
+promise_test(t => {
+  let anim;
+  return getXHRDoc(t).then(xhrdoc => {
+    const div = addDiv(t);
+    anim = div.animate({ opacity: [ 0, 1 ] }, 1000);
+    assert_equals(getComputedStyle(div).opacity, '0',
+                  'Style should be updated');
+    // Trigger an animation restyle to be queued
+    anim.currentTime = 0.1;
+    // Adopt node into XHR doc
+    xhrdoc.body.appendChild(div);
+    // We should skip applying animation styles to elements in documents
+    // without a pres shell.
+    assert_equals(getComputedStyle(div).opacity, '1',
+                  'Style should NOT be updated');
+  });
+}, 'Moving an element with a pending animation restyle to a document without'
+   + ' a browsing context resets animation style');
+
+</script>
diff --git a/dom/animation/test/mozilla/test_set_easing.html b/dom/animation/test/mozilla/test_set_easing.html
new file mode 100644
index 0000000000..55c77f0e8f
--- /dev/null
+++ b/dom/animation/test/mozilla/test_set_easing.html
@@ -0,0 +1,36 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Test setting easing in sandbox</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+</head>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+test(function(t) {
+  const div = document.createElement("div");
+  document.body.appendChild(div);
+  div.animate({ opacity: [0, 1] }, 100000 );
+
+  const contentScript = function() {
+    try {
+      document.getAnimations()[0].effect.updateTiming({ easing: 'linear' });
+      assert_true(true, 'Setting easing should not throw in sandbox');
+    } catch (e) {
+      assert_unreached('Setting easing threw ' + e);
+    }
+  };
+
+  const sandbox = new SpecialPowers.Cu.Sandbox(window);
+  sandbox.importFunction(document, "document");
+  sandbox.importFunction(assert_true, "assert_true");
+  sandbox.importFunction(assert_unreached, "assert_unreached");
+  SpecialPowers.Cu.evalInSandbox(`(${contentScript.toString()})()`, sandbox);
+}, 'Setting easing should not throw any exceptions in sandbox');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_style_after_finished_on_compositor.html b/dom/animation/test/mozilla/test_style_after_finished_on_compositor.html
new file mode 100644
index 0000000000..bccae9e0d5
--- /dev/null
+++ b/dom/animation/test/mozilla/test_style_after_finished_on_compositor.html
@@ -0,0 +1,138 @@
+<!doctype html>
+<head>
+<meta charset=utf-8>
+<title>Test for styles after finished on the compositor</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<style>
+.compositor {
+  /* Element needs geometry to be eligible for layerization */
+  width: 100px;
+  height: 100px;
+  background-color: green;
+}
+</style>
+</head>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+promise_test(async t => {
+  const div = addDiv(t, { 'class': 'compositor' });
+  const anim = div.animate([ { offset: 0, opacity: 1 },
+                             { offset: 1, opacity: 0 } ],
+                           { delay: 10,
+                             duration: 100 });
+
+  await anim.finished;
+
+  await waitForNextFrame();
+
+  const opacity = SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+
+  assert_equals(opacity, '', 'No opacity animation runs on the compositor');
+}, 'Opacity animation with positive delay is removed from compositor when ' +
+   'finished');
+
+promise_test(async t => {
+  const div = addDiv(t, { 'class': 'compositor' });
+  const anim = div.animate([ { offset: 0,   opacity: 1 },
+                             { offset: 0.9, opacity: 1 },
+                             { offset: 1,   opacity: 0 } ],
+                           { duration: 100 });
+
+  await anim.finished;
+
+  await waitForNextFrame();
+
+  const opacity = SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+
+  assert_equals(opacity, '', 'No opacity animation runs on the compositor');
+}, 'Opacity animation initially opacity: 1 is removed from compositor when ' +
+   'finished');
+
+promise_test(async t => {
+  const div = addDiv(t, { 'class': 'compositor' });
+  const anim = div.animate([ { offset: 0,    opacity: 0 },
+                             { offset: 0.5,  opacity: 1 },
+                             { offset: 0.51, opacity: 1 },
+                             { offset: 1,    opacity: 0 } ],
+                           { delay: 10, duration: 100 });
+
+  await waitForAnimationFrames(2);
+
+  // Setting the current time at the offset generating opacity: 1.
+  anim.currentTime = 60;
+
+  await anim.finished;
+
+  await waitForNextFrame();
+
+  const opacity = SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+
+  assert_equals(opacity, '', 'No opacity animation runs on the compositor');
+}, 'Opacity animation is removed from compositor even when it only visits ' +
+   'exactly the point where the opacity: 1 value was set');
+
+promise_test(async t => {
+  const div = addDiv(t, { 'class': 'compositor' });
+  const anim = div.animate([ { offset: 0, transform: 'none' },
+                             { offset: 1, transform: 'translateX(100px)' } ],
+                           { delay: 10,
+                             duration: 100 });
+
+  await anim.finished;
+
+  await waitForNextFrame();
+
+  const transform = SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+
+  assert_equals(transform, '', 'No transform animation runs on the compositor');
+}, 'Transform animation with positive delay is removed from compositor when ' +
+   'finished');
+
+promise_test(async t => {
+  const div = addDiv(t, { 'class': 'compositor' });
+  const anim = div.animate([ { offset: 0,   transform: 'none' },
+                             { offset: 0.9, transform: 'none' },
+                             { offset: 1,   transform: 'translateX(100px)' } ],
+                           { duration: 100 });
+
+  await anim.finished;
+
+  await waitForNextFrame();
+
+  const transform = SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+
+  assert_equals(transform, '', 'No transform animation runs on the compositor');
+}, 'Transform animation initially transform: none is removed from compositor ' +
+   'when finished');
+
+
+promise_test(async t => {
+  const div = addDiv(t, { 'class': 'compositor' });
+  const anim = div.animate([ { offset: 0,   transform: 'translateX(100px)' },
+                             { offset: 0.5, transform: 'none' },
+                             { offset: 0.9, transform: 'none' },
+                             { offset: 1,   transform: 'translateX(100px)' } ],
+                           { delay: 10, duration: 100 });
+
+  await waitForAnimationFrames(2);
+
+  // Setting the current time at the offset generating transform: none.
+  anim.currentTime = 60;
+
+  await anim.finished;
+
+  await waitForNextFrame();
+
+  const transform = SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+
+  assert_equals(transform, '', 'No transform animation runs on the compositor');
+}, 'Transform animation is removed from compositor even when it only visits ' +
+   'exactly the point where the transform: none value was set');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_transform_limits.html b/dom/animation/test/mozilla/test_transform_limits.html
new file mode 100644
index 0000000000..92d1b7e1ec
--- /dev/null
+++ b/dom/animation/test/mozilla/test_transform_limits.html
@@ -0,0 +1,56 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+// We clamp +infinity or -inifinity value in floating point to
+// maximum floating point value or -maximum floating point value.
+const MAX_FLOAT = 3.40282e+38;
+
+test(function(t) {
+  var div = addDiv(t);
+  div.style = "width: 1px; height: 1px;";
+  var anim = div.animate([ { transform: 'scale(1)' },
+                           { transform: 'scale(3.5e+38)'},
+                           { transform: 'scale(3)' } ], 100 * MS_PER_SEC);
+
+  anim.pause();
+  anim.currentTime = 50 * MS_PER_SEC;
+  assert_equals(getComputedStyle(div).transform,
+                'matrix(' + MAX_FLOAT + ', 0, 0, ' + MAX_FLOAT + ', 0, 0)');
+}, 'Test that the parameter of transform scale is clamped' );
+
+test(function(t) {
+  var div = addDiv(t);
+  div.style = "width: 1px; height: 1px;";
+  var anim = div.animate([ { transform: 'translate(1px)' },
+                           { transform: 'translate(3.5e+38px)'},
+                           { transform: 'translate(3px)' } ], 100 * MS_PER_SEC);
+
+  anim.pause();
+  anim.currentTime = 50 * MS_PER_SEC;
+  assert_equals(getComputedStyle(div).transform,
+                'matrix(1, 0, 0, 1, ' + MAX_FLOAT + ', 0)');
+}, 'Test that the parameter of transform translate is clamped' );
+
+test(function(t) {
+  var div = addDiv(t);
+  div.style = "width: 1px; height: 1px;";
+  var anim = div.animate([ { transform: 'matrix(0.5, 0, 0, 0.5, 0, 0)' },
+                           { transform: 'matrix(2, 0, 0, 2, 3.5e+38, 0)'},
+                           { transform: 'matrix(0, 2, 0, -2, 0, 0)' } ],
+                         100 * MS_PER_SEC);
+
+  anim.pause();
+  anim.currentTime = 50 * MS_PER_SEC;
+  assert_equals(getComputedStyle(div).transform,
+                'matrix(2, 0, 0, 2, ' + MAX_FLOAT + ', 0)');
+}, 'Test that the parameter of transform matrix is clamped' );
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_transition_finish_on_compositor.html b/dom/animation/test/mozilla/test_transition_finish_on_compositor.html
new file mode 100644
index 0000000000..46a154b9af
--- /dev/null
+++ b/dom/animation/test/mozilla/test_transition_finish_on_compositor.html
@@ -0,0 +1,22 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+'use strict';
+setup({explicit_done: true});
+// This test appears like it might get racey and cause a timeout with too low of a
+// precision, so we hardcode it to something reasonable.
+SpecialPowers.pushPrefEnv(
+  {
+    set: [
+      ['privacy.reduceTimerPrecision', true],
+      ['privacy.resistFingerprinting.reduceTimerPrecision.microseconds', 2000],
+    ],
+  },
+  function() {
+    window.open('file_transition_finish_on_compositor.html');
+  }
+);
+</script>
diff --git a/dom/animation/test/mozilla/test_underlying_discrete_value.html b/dom/animation/test/mozilla/test_underlying_discrete_value.html
new file mode 100644
index 0000000000..3961305df3
--- /dev/null
+++ b/dom/animation/test/mozilla/test_underlying_discrete_value.html
@@ -0,0 +1,188 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+// Tests that we correctly extract the underlying value when the animation
+// type is 'discrete'.
+const discreteTests = [
+  {
+    stylesheet: {
+      "@keyframes keyframes":
+      "from { align-content: flex-start; } to { align-content: flex-end; } "
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "flex-start" },
+      { computedOffset: 1, alignContent: "flex-end" }
+    ],
+    explanation: "Test for fully-specified keyframes"
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "from { align-content: flex-start; }"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "flex-start" },
+      { computedOffset: 1, alignContent: "normal" }
+    ],
+    explanation: "Test for 0% keyframe only",
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "to { align-content: flex-end; }"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "normal" },
+      { computedOffset: 1, alignContent: "flex-end" }
+    ],
+    explanation: "Test for 100% keyframe only",
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "50% { align-content: center; }",
+      "#target": "align-content: space-between;"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "space-between" },
+      { computedOffset: 0.5, alignContent: "center" },
+      { computedOffset: 1, alignContent: "space-between" }
+    ],
+    explanation: "Test for no 0%/100% keyframes " +
+                 "and specified style on target element"
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "50% { align-content: center; }"
+    },
+    attributes: {
+      style: "align-content: space-between"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "space-between" },
+      { computedOffset: 0.5, alignContent: "center" },
+      { computedOffset: 1, alignContent: "space-between" }
+    ],
+    explanation: "Test for no 0%/100% keyframes " +
+                 "and specified style on target element using style attribute"
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "50% { align-content: center; }",
+      "#target": "align-content: inherit;"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "normal" },
+      { computedOffset: 0.5, alignContent: "center" },
+      { computedOffset: 1, alignContent: "normal" }
+    ],
+    explanation: "Test for no 0%/100% keyframes " +
+                 "and 'inherit' specified on target element",
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "50% { align-content: center; }",
+      ".target": "align-content: space-between;"
+    },
+    attributes: {
+      class: "target"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "space-between" },
+      { computedOffset: 0.5, alignContent: "center" },
+      { computedOffset: 1, alignContent: "space-between" }
+    ],
+    explanation: "Test for no 0%/100% keyframes " +
+                 "and specified style on target element using class selector"
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "50% { align-content: center; }",
+      "div": "align-content: space-between;"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "space-between" },
+      { computedOffset: 0.5, alignContent: "center" },
+      { computedOffset: 1, alignContent: "space-between" }
+    ],
+    explanation: "Test for no 0%/100% keyframes " +
+                 "and specified style on target element using type selector"
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "50% { align-content: center; }",
+      "div": "align-content: space-between;",
+      ".target": "align-content: flex-start;",
+      "#target": "align-content: flex-end;"
+    },
+    attributes: {
+      class: "target"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "flex-end" },
+      { computedOffset: 0.5, alignContent: "center" },
+      { computedOffset: 1, alignContent: "flex-end" }
+    ],
+    explanation: "Test for no 0%/100% keyframes " +
+                 "and specified style on target element " +
+                 "using ID selector that overrides class selector"
+  },
+  {
+    stylesheet: {
+      "@keyframes keyframes": "50% { align-content: center; }",
+      "div": "align-content: space-between !important;",
+      ".target": "align-content: flex-start;",
+      "#target": "align-content: flex-end;"
+    },
+    attributes: {
+      class: "target"
+    },
+    expectedKeyframes: [
+      { computedOffset: 0, alignContent: "space-between" },
+      { computedOffset: 0.5, alignContent: "center" },
+      { computedOffset: 1, alignContent: "space-between" }
+    ],
+    explanation: "Test for no 0%/100% keyframes " +
+                 "and specified style on target element " +
+                 "using important type selector that overrides other rules"
+  },
+];
+
+discreteTests.forEach(testcase => {
+  test(t => {
+    if (testcase.skip) {
+      return;
+    }
+    addStyle(t, testcase.stylesheet);
+
+    const div = addDiv(t, { "id": "target" });
+    if (testcase.attributes) {
+      for (let attributeName in testcase.attributes) {
+        div.setAttribute(attributeName, testcase.attributes[attributeName]);
+      }
+    }
+    div.style.animation = "keyframes 100s";
+
+    const keyframes = div.getAnimations()[0].effect.getKeyframes();
+    const expectedKeyframes = testcase.expectedKeyframes;
+    assert_equals(keyframes.length, expectedKeyframes.length,
+                  `keyframes.length should be ${ expectedKeyframes.length }`);
+
+    keyframes.forEach((keyframe, index) => {
+      const expectedKeyframe = expectedKeyframes[index];
+      assert_equals(keyframe.computedOffset, expectedKeyframe.computedOffset,
+                    `computedOffset of keyframes[${ index }] should be ` +
+                    `${ expectedKeyframe.computedOffset }`);
+      assert_equals(keyframe.alignContent, expectedKeyframe.alignContent,
+                    `alignContent of keyframes[${ index }] should be ` +
+                    `${ expectedKeyframe.alignContent }`);
+    });
+  }, testcase.explanation);
+});
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/test_unstyled.html b/dom/animation/test/mozilla/test_unstyled.html
new file mode 100644
index 0000000000..4724979c11
--- /dev/null
+++ b/dom/animation/test/mozilla/test_unstyled.html
@@ -0,0 +1,54 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<style>
+div.pseudo::before {
+  animation: animation 1s;
+  content: 'content';
+}
+@keyframes animation {
+  to { opacity: 0 }
+}
+</style>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+// Tests for cases where we may not have style data for an element
+
+promise_test(async t => {
+  // Get a CSSPseudoElement
+  const div = addDiv(t, { class: 'pseudo' });
+  const cssAnim = document.getAnimations()[0];
+  const pseudoElem = cssAnim.effect.target;
+
+  // Drop pseudo from styles and flush styles
+  div.classList.remove('pseudo');
+  getComputedStyle(div, '::before').content;
+
+  // Try animating the pseudo's content attribute
+  const contentAnim = pseudoElem.animate(
+    { content: ['none', '"content"'] },
+    { duration: 100 * MS_PER_SEC, fill: 'both' }
+  );
+
+  // Check that the initial value is as expected
+  await contentAnim.ready;
+  assert_equals(getComputedStyle(div, '::before').content, 'none');
+
+  contentAnim.finish();
+
+  // Animating an obsolete pseudo element should NOT cause the pseudo element
+  // to be re-generated. That behavior might change in which case this test
+  // will need to be updated. The most important part of this test, however,
+  // is simply checking that nothing explodes if we try to animate such a
+  // pseudo element.
+
+  assert_equals(getComputedStyle(div, '::before').content, 'none');
+}, 'Animation on an obsolete pseudo element produces expected results');
+
+</script>
+</body>
diff --git a/dom/animation/test/mozilla/xhr_doc.html b/dom/animation/test/mozilla/xhr_doc.html
new file mode 100644
index 0000000000..b9fa57e3f5
--- /dev/null
+++ b/dom/animation/test/mozilla/xhr_doc.html
@@ -0,0 +1,2 @@
+<!doctype html>
+<div id=test></div>
diff --git a/dom/animation/test/style/test_animation-seeking-with-current-time.html b/dom/animation/test/style/test_animation-seeking-with-current-time.html
new file mode 100644
index 0000000000..265de8f0f5
--- /dev/null
+++ b/dom/animation/test/style/test_animation-seeking-with-current-time.html
@@ -0,0 +1,123 @@
+<!doctype html>
+<html>
+  <head>
+    <meta charset=utf-8>
+    <title>Tests for seeking using Animation.currentTime</title>
+    <style>
+.animated-div {
+  margin-left: -10px;
+  animation-timing-function: linear ! important;
+}
+
+@keyframes anim {
+  from { margin-left: 0px; }
+  to { margin-left: 100px; }
+}
+    </style>
+    <script src="/resources/testharness.js"></script>
+    <script src="/resources/testharnessreport.js"></script>
+    <script src="../testcommon.js"></script>
+  </head>
+  <body>
+    <div id="log"></div>
+    <script type="text/javascript">
+'use strict';
+
+function assert_marginLeft_equals(target, expect, description) {
+  var marginLeft = parseFloat(getComputedStyle(target).marginLeft);
+  assert_equals(marginLeft, expect, description);
+}
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    animation.currentTime = 90 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 90,
+      'Computed style is updated when seeking forwards in active interval');
+
+    animation.currentTime = 10 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 10,
+      'Computed style is updated when seeking backwards in active interval');
+  });
+}, 'Seeking forwards and backward in active interval');
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    assert_marginLeft_equals(div, -10,
+      'Computed style is unaffected in before phase with no backwards fill');
+
+    // before -> active (non-active -> active)
+    animation.currentTime = 150 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 50,
+      'Computed style is updated when seeking forwards from ' +
+      'not \'in effect\' to \'in effect\' state');
+  });
+}, 'Seeking to non-\'in effect\' from \'in effect\' (before -> active)');
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    // move to after phase
+    animation.currentTime = 250 * MS_PER_SEC;
+    assert_marginLeft_equals(div, -10,
+      'Computed style is unaffected in after phase with no forwards fill');
+
+    // after -> active (non-active -> active)
+    animation.currentTime = 150 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 50,
+      'Computed style is updated when seeking backwards from ' +
+      'not \'in effect\' to \'in effect\' state');
+  });
+}, 'Seeking to non-\'in effect\' from \'in effect\' (after -> active)');
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    // move to active phase
+    animation.currentTime = 150 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 50,
+      'Computed value is set during active phase');
+
+    // active -> before
+    animation.currentTime = 50 * MS_PER_SEC;
+    assert_marginLeft_equals(div, -10,
+      'Computed value is not effected after seeking backwards from ' +
+      '\'in effect\' to not \'in effect\' state');
+  });
+}, 'Seeking to \'in effect\' from non-\'in effect\' (active -> before)');
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    // move to active phase
+    animation.currentTime = 150 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 50,
+      'Computed value is set during active phase');
+
+    // active -> after
+    animation.currentTime = 250 * MS_PER_SEC;
+    assert_marginLeft_equals(div, -10,
+      'Computed value is not affected after seeking forwards from ' +
+      '\'in effect\' to not \'in effect\' state');
+  });
+}, 'Seeking to \'in effect\' from non-\'in effect\' (active -> after)');
+
+    </script>
+  </body>
+</html>
diff --git a/dom/animation/test/style/test_animation-seeking-with-start-time.html b/dom/animation/test/style/test_animation-seeking-with-start-time.html
new file mode 100644
index 0000000000..e56db5f23d
--- /dev/null
+++ b/dom/animation/test/style/test_animation-seeking-with-start-time.html
@@ -0,0 +1,123 @@
+<!doctype html>
+<html>
+  <head>
+    <meta charset=utf-8>
+    <title>Tests for seeking using Animation.startTime</title>
+    <style>
+.animated-div {
+  margin-left: -10px;
+  animation-timing-function: linear ! important;
+}
+
+@keyframes anim {
+  from { margin-left: 0px; }
+  to { margin-left: 100px; }
+}
+    </style>
+    <script src="/resources/testharness.js"></script>
+    <script src="/resources/testharnessreport.js"></script>
+    <script src="../testcommon.js"></script>
+  </head>
+  <body>
+    <div id="log"></div>
+    <script type="text/javascript">
+'use strict';
+
+function assert_marginLeft_equals(target, expect, description) {
+  var marginLeft = parseFloat(getComputedStyle(target).marginLeft);
+  assert_equals(marginLeft, expect, description);
+}
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+   animation.startTime = animation.timeline.currentTime - 90 * MS_PER_SEC
+    assert_marginLeft_equals(div, 90,
+      'Computed style is updated when seeking forwards in active interval');
+
+    animation.startTime = animation.timeline.currentTime - 10 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 10,
+      'Computed style is updated when seeking backwards in active interval');
+  });
+}, 'Seeking forwards and backward in active interval');
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    assert_marginLeft_equals(div, -10,
+      'Computed style is unaffected in before phase with no backwards fill');
+
+    // before -> active (non-active -> active)
+    animation.startTime = animation.timeline.currentTime - 150 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 50,
+      'Computed style is updated when seeking forwards from ' +
+      'not \'in effect\' to \'in effect\' state');
+  });
+}, 'Seeking to non-\'in effect\' from \'in effect\' (before -> active)');
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    // move to after phase
+    animation.startTime = animation.timeline.currentTime - 250 * MS_PER_SEC;
+    assert_marginLeft_equals(div, -10,
+      'Computed style is unaffected in after phase with no forwards fill');
+
+    // after -> active (non-active -> active)
+    animation.startTime = animation.timeline.currentTime - 150 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 50,
+      'Computed style is updated when seeking backwards from ' +
+      'not \'in effect\' to \'in effect\' state');
+  });
+}, 'Seeking to non-\'in effect\' from \'in effect\' (after -> active)');
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    // move to active phase
+    animation.startTime = animation.timeline.currentTime - 150 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 50,
+      'Computed value is set during active phase');
+
+    // active -> before
+    animation.startTime = animation.timeline.currentTime - 50 * MS_PER_SEC;
+    assert_marginLeft_equals(div, -10,
+      'Computed value is not affected after seeking backwards from ' +
+      '\'in effect\' to not \'in effect\' state');
+  });
+}, 'Seeking to \'in effect\' from non-\'in effect\' (active -> before)');
+
+promise_test(function(t) {
+  var div = addDiv(t, {'class': 'animated-div'});
+  div.style.animation = "anim 100s 100s";
+  var animation = div.getAnimations()[0];
+
+  return animation.ready.then(function() {
+    // move to active phase
+    animation.startTime = animation.timeline.currentTime - 150 * MS_PER_SEC;
+    assert_marginLeft_equals(div, 50,
+      'Computed value is set during active phase');
+
+    // active -> after
+    animation.startTime = animation.timeline.currentTime - 250 * MS_PER_SEC;
+    assert_marginLeft_equals(div, -10,
+      'Computed value is not affected after seeking forwards from ' +
+      '\'in effect\' to not \'in effect\' state');
+  });
+}, 'Seeking to \'in effect\' from non-\'in effect\' (active -> after)');
+
+    </script>
+  </body>
+</html>
diff --git a/dom/animation/test/style/test_animation-setting-effect.html b/dom/animation/test/style/test_animation-setting-effect.html
new file mode 100644
index 0000000000..8712072a51
--- /dev/null
+++ b/dom/animation/test/style/test_animation-setting-effect.html
@@ -0,0 +1,127 @@
+<!doctype html>
+<html>
+  <head>
+    <meta charset=utf-8>
+    <title>Tests for setting effects by using Animation.effect</title>
+    <script src="/resources/testharness.js"></script>
+    <script src="/resources/testharnessreport.js"></script>
+    <script src='../testcommon.js'></script>
+  </head>
+  <body>
+    <div id="log"></div>
+    <script type='text/javascript'>
+
+'use strict';
+
+test(function(t) {
+  var target = addDiv(t);
+  var anim = new Animation();
+  anim.effect = new KeyframeEffect(target,
+                                   { marginLeft: [ '0px', '100px' ] },
+                                   100 * MS_PER_SEC);
+  anim.currentTime = 50 * MS_PER_SEC;
+  assert_equals(getComputedStyle(target).marginLeft, '50px');
+}, 'After setting target effect on an animation with null effect, the ' +
+   'animation still works');
+
+test(function(t) {
+  var target = addDiv(t);
+  target.style.marginLeft = '10px';
+  var anim = target.animate({ marginLeft: [ '0px', '100px' ] },
+                            100 * MS_PER_SEC);
+  anim.currentTime = 50 * MS_PER_SEC;
+  assert_equals(getComputedStyle(target).marginLeft, '50px');
+
+  anim.effect = null;
+  assert_equals(getComputedStyle(target).marginLeft, '10px');
+}, 'After setting null target effect, the computed style of the target ' +
+   'element becomes the initial value');
+
+test(function(t) {
+  var target = addDiv(t);
+  var animA = target.animate({ marginLeft: [ '0px', '100px' ] },
+                             100 * MS_PER_SEC);
+  var animB = new Animation();
+  animA.currentTime = 50 * MS_PER_SEC;
+  animB.currentTime = 20 * MS_PER_SEC;
+  assert_equals(getComputedStyle(target).marginLeft, '50px',
+                'original computed style of the target element');
+
+  animB.effect = animA.effect;
+  assert_equals(getComputedStyle(target).marginLeft, '20px',
+                'new computed style of the target element');
+}, 'After setting the target effect from an existing animation, the computed ' +
+   'style of the target effect should reflect the time of the updated ' +
+   'animation.');
+
+test(function(t) {
+  var target = addDiv(t);
+  target.style.marginTop = '-10px';
+  var animA = target.animate({ marginLeft: [ '0px', '100px' ] },
+                             100 * MS_PER_SEC);
+  var animB = target.animate({ marginTop: [ '0px', '100px' ] },
+                             50 * MS_PER_SEC);
+  animA.currentTime = 50 * MS_PER_SEC;
+  animB.currentTime = 10 * MS_PER_SEC;
+  assert_equals(getComputedStyle(target).marginLeft, '50px',
+                'original margin-left of the target element');
+  assert_equals(getComputedStyle(target).marginTop, '20px',
+                'original margin-top of the target element');
+
+  animB.effect = animA.effect;
+  assert_equals(getComputedStyle(target).marginLeft, '10px',
+                'new margin-left of the target element');
+  assert_equals(getComputedStyle(target).marginTop, '-10px',
+                'new margin-top of the target element');
+}, 'After setting target effect with an animation to another animation which ' +
+   'also has an target effect and both animation effects target to the same ' +
+   'element, the computed style of this element should reflect the time and ' +
+   'effect of the animation that was set');
+
+test(function(t) {
+  var targetA = addDiv(t);
+  var targetB = addDiv(t);
+  targetB.style.marginLeft = '-10px';
+  var animA = targetA.animate({ marginLeft: [ '0px', '100px' ] },
+                              100 * MS_PER_SEC);
+  var animB = targetB.animate({ marginLeft: [ '0px', '100px' ] },
+                              50 * MS_PER_SEC);
+  animA.currentTime = 50 * MS_PER_SEC;
+  animB.currentTime = 10 * MS_PER_SEC;
+  assert_equals(getComputedStyle(targetA).marginLeft, '50px',
+                'original margin-left of the first element');
+  assert_equals(getComputedStyle(targetB).marginLeft, '20px',
+                'original margin-left of the second element');
+
+  animB.effect = animA.effect;
+  assert_equals(getComputedStyle(targetA).marginLeft, '10px',
+                'new margin-left of the first element');
+  assert_equals(getComputedStyle(targetB).marginLeft, '-10px',
+                'new margin-left of the second element');
+}, 'After setting target effect with an animation to another animation which ' +
+   'also has an target effect and these animation effects target to ' +
+   'different elements, the computed styles of the two elements should ' +
+   'reflect the time and effect of the animation that was set');
+
+test(function(t) {
+  var target = addDiv(t);
+  var animA = target.animate({ marginLeft: [ '0px', '100px' ] },
+                             50 * MS_PER_SEC);
+  var animB = target.animate({ marginTop: [ '0px', '50px' ] },
+                             100 * MS_PER_SEC);
+  animA.currentTime = 20 * MS_PER_SEC;
+  animB.currentTime = 30 * MS_PER_SEC;
+  assert_equals(getComputedStyle(target).marginLeft, '40px');
+  assert_equals(getComputedStyle(target).marginTop, '15px');
+
+  var effectA = animA.effect;
+  animA.effect = animB.effect;
+  animB.effect = effectA;
+  assert_equals(getComputedStyle(target).marginLeft, '60px');
+  assert_equals(getComputedStyle(target).marginTop, '10px');
+}, 'After swapping effects of two playing animations, both animations are ' +
+   'still running with the same current time');
+
+    </script>
+  </body>
+</html>
diff --git a/dom/animation/test/style/test_composite.html b/dom/animation/test/style/test_composite.html
new file mode 100644
index 0000000000..1383b1b1e6
--- /dev/null
+++ b/dom/animation/test/style/test_composite.html
@@ -0,0 +1,142 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<style>
+div {
+  /* Element needs geometry to be eligible for layerization */
+  width: 20px;
+  height: 20px;
+  background-color: white;
+}
+</style>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+if (!SpecialPowers.DOMWindowUtils.layerManagerRemote ||
+    !SpecialPowers.getBoolPref(
+      'layers.offmainthreadcomposition.async-animations')) {
+  // If OMTA is disabled, nothing to run.
+  done();
+}
+
+function waitForPaintsFlushed() {
+  return new Promise(function(resolve, reject) {
+    waitForAllPaintsFlushed(resolve);
+  });
+}
+
+promise_test(t => {
+  // Without this, the first test case fails on Android.
+  return waitForDocumentLoad();
+}, 'Ensure document has been loaded');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+    div.animate({ transform: ['translateX(0px)', 'translateX(200px)'],
+                  composite: 'accumulate' },
+                100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 200, 0)',
+      'Transform value at 50%');
+  });
+}, 'Accumulate onto the base value');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    div.animate({ transform: ['translateX(100px)', 'translateX(200px)'],
+                  composite: 'replace' },
+                100 * MS_PER_SEC);
+    div.animate({ transform: ['translateX(0px)', 'translateX(100px)'],
+                  composite: 'accumulate' },
+                100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 200, 0)',
+      'Transform value at 50%');
+  });
+}, 'Accumulate onto an underlying animation value');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+    div.animate([{ transform: 'translateX(100px)', composite: 'accumulate' },
+                 { transform: 'translateX(300px)', composite: 'replace' }],
+                100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 250, 0)',
+      'Transform value at 50s');
+  });
+}, 'Composite when mixing accumulate and replace');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+    div.animate([{ transform: 'translateX(100px)', composite: 'replace' },
+                 { transform: 'translateX(300px)' }],
+                { duration: 100 * MS_PER_SEC, composite: 'accumulate' });
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 250, 0)',
+      'Transform value at 50%');
+  });
+}, 'Composite specified on a keyframe overrides the composite mode of the ' +
+   'effect');
+
+promise_test(t => {
+  var div;
+  var anim;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    div.animate({ transform: [ 'scale(2)', 'scale(2)' ] }, 100 * MS_PER_SEC);
+    anim = div.animate({ transform: [ 'scale(4)', 'scale(4)' ] },
+                       { duration: 100 * MS_PER_SEC, composite: 'add' });
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(8, 0, 0, 8, 0, 0)',
+      'The additive scale value should be scale(8)'); // scale(2) scale(4)
+
+    anim.effect.composite = 'accumulate';
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(1);
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(5, 0, 0, 5, 0, 0)',
+      // (scale(2 - 1) + scale(4 - 1) + scale(1))
+      'The accumulate scale value should be scale(5)');
+  });
+}, 'Composite operation change');
+
+</script>
+</body>
diff --git a/dom/animation/test/style/test_interpolation-from-interpolatematrix-to-none.html b/dom/animation/test/style/test_interpolation-from-interpolatematrix-to-none.html
new file mode 100644
index 0000000000..1da95392eb
--- /dev/null
+++ b/dom/animation/test/style/test_interpolation-from-interpolatematrix-to-none.html
@@ -0,0 +1,43 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src='/resources/testharness.js'></script>
+<script src='/resources/testharnessreport.js'></script>
+<script src='../testcommon.js'></script>
+<div id='log'></div>
+<script type='text/javascript'>
+'use strict';
+
+test(function(t) {
+  var target = addDiv(t);
+  target.style.transform = 'translateX(100px)';
+  target.style.transition = 'all 10s linear -5s';
+  getComputedStyle(target).transform;
+
+  target.style.transform = 'rotate(90deg)';
+  var interpolated_matrix = 'matrix(' + Math.cos(Math.PI / 4) + ',' +
+                                        Math.sin(Math.PI / 4) + ',' +
+                                       -Math.sin(Math.PI / 4) + ',' +
+                                        Math.cos(Math.PI / 4) + ',' +
+                                        '50, 0)';
+  assert_matrix_equals(getComputedStyle(target).transform,
+                       interpolated_matrix,
+                       'the equivalent matrix of ' + 'interpolatematrix(' +
+                       'translateX(100px), rotate(90deg), 0.5)');
+
+  // Trigger a new transition from
+  // interpolatematrix(translateX(100px), rotate(90deg), 0.5) to none
+  // with 'all 10s linear -5s'.
+  target.style.transform = 'none';
+  interpolated_matrix = 'matrix(' + Math.cos(Math.PI / 8) + ',' +
+                                    Math.sin(Math.PI / 8) + ',' +
+                                   -Math.sin(Math.PI / 8) + ',' +
+                                    Math.cos(Math.PI / 8) + ',' +
+                                    '25, 0)';
+  assert_matrix_equals(getComputedStyle(target).transform,
+                       interpolated_matrix,
+                       'the expected matrix from interpolatematrix(' +
+                       'translateX(100px), rotate(90deg), 0.5) to none at 50%');
+}, 'Test interpolation from interpolatematrix to none at 50%');
+
+</script>
+</html>
diff --git a/dom/animation/test/style/test_missing-keyframe-on-compositor.html b/dom/animation/test/style/test_missing-keyframe-on-compositor.html
new file mode 100644
index 0000000000..8b92a89168
--- /dev/null
+++ b/dom/animation/test/style/test_missing-keyframe-on-compositor.html
@@ -0,0 +1,577 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<style>
+div {
+  /* Element needs geometry to be eligible for layerization */
+  width: 100px;
+  height: 100px;
+  background-color: white;
+}
+</style>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+if (!SpecialPowers.DOMWindowUtils.layerManagerRemote ||
+    !SpecialPowers.getBoolPref(
+      'layers.offmainthreadcomposition.async-animations')) {
+  // If OMTA is disabled, nothing to run.
+  done();
+}
+
+function waitForPaintsFlushed() {
+  return new Promise(function(resolve, reject) {
+    waitForAllPaintsFlushed(resolve);
+  });
+}
+
+// Note that promise tests run in sequence so this ensures the document is
+// loaded before any of the other tests run.
+promise_test(t => {
+  // Without this, the first test case fails on Android.
+  return waitForDocumentLoad();
+}, 'Ensure document has been loaded');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'opacity: 0.1' });
+    div.animate({ opacity: 1 }, 100 * MS_PER_SEC);
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    assert_equals(opacity, '0.1',
+                  'The initial opacity value should be the base value');
+  });
+}, 'Initial opacity value for animation with no no keyframe at offset 0');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'opacity: 0.1' });
+    div.animate({ opacity: [ 0.5, 1 ] }, 100 * MS_PER_SEC);
+    div.animate({ opacity: 1 }, 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    assert_equals(opacity, '0.5',
+                  'The initial opacity value should be the value of ' +
+                  'lower-priority animation value');
+  });
+}, 'Initial opacity value for animation with no keyframe at offset 0 when ' +
+   'there is a lower-priority animation');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'opacity: 0.1; transition: opacity 100s linear' });
+    getComputedStyle(div).opacity;
+
+    div.style.opacity = '0.5';
+    getComputedStyle(div).opacity;
+
+    div.animate({ opacity: 1 }, 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    assert_equals(opacity, '0.1',
+                  'The initial opacity value should be the initial value of ' +
+                  'the transition');
+  });
+}, 'Initial opacity value for animation with no keyframe at offset 0 when ' +
+   'there is a transition on the same property');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'opacity: 0' });
+    div.animate([{ offset: 0, opacity: 1 }], 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    assert_equals(opacity, '0.5',
+                  'Opacity value at 50% should be composed onto the base ' +
+                  'value');
+  });
+}, 'Opacity value for animation with no keyframe at offset 1 at 50% ');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'opacity: 0' });
+    div.animate({ opacity: [ 0.5, 0.5 ] }, 100 * MS_PER_SEC);
+    div.animate([{ offset: 0, opacity: 1 }], 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    assert_equals(opacity, '0.75', // (0.5 + 1) * 0.5
+                  'Opacity value at 50% should be composed onto the value ' +
+                  'of middle of lower-priority animation');
+  });
+}, 'Opacity value for animation with no keyframe at offset 1 at 50% when ' +
+   'there is a lower-priority animation');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'opacity: 0; transition: opacity 100s linear' });
+    getComputedStyle(div).opacity;
+
+    div.style.opacity = '0.5';
+    getComputedStyle(div).opacity;
+
+    div.animate([{ offset: 0, opacity: 1 }], 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    assert_equals(opacity, '0.625', // ((0 + 0.5) * 0.5 + 1) * 0.5
+                  'Opacity value at 50% should be composed onto the value ' +
+                  'of middle of transition');
+  });
+}, 'Opacity value for animation with no keyframe at offset 1 at 50% when ' +
+   'there is a transition on the same property');
+
+promise_test(t => {
+  var div;
+  var lowerAnimation;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    lowerAnimation = div.animate({ opacity: [ 0.5, 1 ] }, 100 * MS_PER_SEC);
+    var higherAnimation = div.animate({ opacity: 1 }, 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    lowerAnimation.pause();
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    // The underlying value is the value that is staying at 0ms of the
+    // lowerAnimation, that is 0.5.
+    // (0.5 + 1.0) * (50 * MS_PER_SEC / 100 * MS_PER_SEC) = 0.75.
+    assert_equals(opacity, '0.75',
+                  'Composed opacity value should be composed onto the value ' +
+                  'of lower-priority paused animation');
+  });
+}, 'Opacity value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto a paused underlying animation');
+
+promise_test(t => {
+  var div;
+  var lowerAnimation;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    lowerAnimation = div.animate({ opacity: [ 0.5, 1 ] }, 100 * MS_PER_SEC);
+    var higherAnimation = div.animate({ opacity: 1 }, 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    lowerAnimation.playbackRate = 0;
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    // The underlying value is the value that is staying at 0ms of the
+    // lowerAnimation, that is 0.5.
+    // (0.5 + 1.0) * (50 * MS_PER_SEC / 100 * MS_PER_SEC) = 0.75.
+    assert_equals(opacity, '0.75',
+                  'Composed opacity value should be composed onto the value ' +
+                  'of lower-priority zero playback rate animation');
+  });
+}, 'Opacity value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto a zero playback rate underlying animation');
+
+promise_test(t => {
+  var div;
+  var lowerAnimation;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    lowerAnimation = div.animate({ opacity: [ 1, 0.5 ] }, 100 * MS_PER_SEC);
+    var higherAnimation = div.animate({ opacity: 1 }, 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    lowerAnimation.effect.updateTiming({
+      duration: 0,
+      fill: 'forwards',
+    });
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var opacity =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'opacity');
+    // The underlying value is the value that is filling forwards state of the
+    // lowerAnimation, that is 0.5.
+    // (0.5 + 1.0) * (50 * MS_PER_SEC / 100 * MS_PER_SEC) = 0.75.
+    assert_equals(opacity, '0.75',
+                  'Composed opacity value should be composed onto the value ' +
+                  'of lower-priority zero active duration animation');
+  });
+}, 'Opacity value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto a zero active duration underlying animation');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+    div.animate({ transform: 'translateX(200px)' }, 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 100, 0)',
+      'The initial transform value should be the base value');
+  });
+}, 'Initial transform value for animation with no keyframe at offset 0');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+    div.animate({ transform: [ 'translateX(200px)', 'translateX(300px)' ] },
+                100 * MS_PER_SEC);
+    div.animate({ transform: 'translateX(400px)' }, 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 200, 0)',
+      'The initial transform value should be lower-priority animation value');
+  });
+}, 'Initial transform value for animation with no keyframe at offset 0 when ' +
+   'there is a lower-priority animation');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px);' +
+                             'transition: transform 100s linear' });
+    getComputedStyle(div).transform;
+
+    div.style.transform = 'translateX(200px)';
+    getComputedStyle(div).transform;
+
+    div.animate({ transform: 'translateX(400px)' }, 100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 100, 0)',
+      'The initial transform value should be the initial value of the ' +
+      'transition');
+  });
+}, 'Initial transform value for animation with no keyframe at offset 0 when ' +
+   'there is a transition');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+    div.animate([{ offset: 0, transform: 'translateX(200pX)' }],
+                100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 150, 0)',
+      'Transform value at 50% should be the base value');
+  });
+}, 'Transform value for animation with no keyframe at offset 1 at 50%');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+    div.animate({ transform: [ 'translateX(200px)', 'translateX(200px)' ] },
+                100 * MS_PER_SEC);
+    div.animate([{ offset: 0, transform: 'translateX(300px)' }],
+                100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 250, 0)',
+      'The final transform value should be the base value');
+  });
+}, 'Transform value for animation with no keyframe at offset 1 at 50% when ' +
+   'there is a lower-priority animation');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px);' +
+                             'transition: transform 100s linear' });
+    getComputedStyle(div).transform;
+
+    div.style.transform = 'translateX(200px)';
+    getComputedStyle(div).transform;
+
+    div.animate([{ offset: 0, transform: 'translateX(300px)' }],
+                100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+                                                   // (150px + 300px) * 0.5
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 225, 0)',
+      'The final transform value should be the final value of the transition');
+  });
+}, 'Transform value for animation with no keyframe at offset 1 at 50% when ' +
+   'there is a transition');
+
+promise_test(t => {
+  var div;
+  var lowerAnimation;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    lowerAnimation =
+      div.animate({ transform: [ 'translateX(100px)', 'translateX(200px)' ] },
+                  100 * MS_PER_SEC);
+    var higherAnimation = div.animate({ transform: 'translateX(300px)' },
+                                      100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    lowerAnimation.pause();
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    // The underlying value is the value that is staying at 0ms of the
+    // lowerAnimation, that is 100px.
+    // (100px + 300px) * (50 * MS_PER_SEC / 100 * MS_PER_SEC) = 200px.
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 200, 0)',
+      'Composed transform value should be composed onto the value of ' +
+      'lower-priority paused animation');
+  });
+}, 'Transform value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto a paused underlying animation');
+
+promise_test(t => {
+  var div;
+  var lowerAnimation;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    lowerAnimation =
+      div.animate({ transform: [ 'translateX(100px)', 'translateX(200px)' ] },
+                  100 * MS_PER_SEC);
+    var higherAnimation = div.animate({ transform: 'translateX(300px)' },
+                                      100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    lowerAnimation.playbackRate = 0;
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    // The underlying value is the value that is staying at 0ms of the
+    // lowerAnimation, that is 100px.
+    // (100px + 300px) * (50 * MS_PER_SEC / 100 * MS_PER_SEC) = 200px.
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 200, 0)',
+      'Composed transform value should be composed onto the value of ' +
+      'lower-priority zero playback rate animation');
+  });
+}, 'Transform value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto a zero playback rate underlying animation');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    var lowerAnimation =
+      div.animate({ transform: [ 'translateX(100px)', 'translateX(200px)' ] },
+                  { duration: 10 * MS_PER_SEC,
+                    fill: 'forwards' });
+    var higherAnimation = div.animate({ transform: 'translateX(300px)' },
+                                      100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    // We need to wait for a paint so that we can send the state of the lower
+    // animation that is actually finished at this point.
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    // (200px + 300px) * (50 * MS_PER_SEC / 100 * MS_PER_SEC) = 250px.
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 250, 0)',
+      'Composed transform value should be composed onto the value of ' +
+      'lower-priority animation with fill:forwards');
+  });
+}, 'Transform value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto a underlying animation with fill:forwards');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    var lowerAnimation =
+      div.animate({ transform: [ 'translateX(100px)', 'translateX(200px)' ] },
+                  { duration: 10 * MS_PER_SEC,
+                    endDelay: -5 * MS_PER_SEC,
+                    fill: 'forwards' });
+    var higherAnimation = div.animate({ transform: 'translateX(300px)' },
+                                      100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    // We need to wait for a paint just like the above test.
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    // (150px + 300px) * (50 * MS_PER_SEC / 100 * MS_PER_SEC) = 225px.
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 225, 0)',
+      'Composed transform value should be composed onto the value of ' +
+      'lower-priority animation with fill:forwards and negative endDelay');
+  });
+}, 'Transform value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto a underlying animation with fill:forwards and negative ' +
+   'endDelay');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    var lowerAnimation =
+      div.animate({ transform: [ 'translateX(100px)', 'translateX(200px)' ] },
+                  { duration: 10 * MS_PER_SEC,
+                    endDelay: 100 * MS_PER_SEC,
+                    fill: 'forwards' });
+    var higherAnimation = div.animate({ transform: 'translateX(300px)' },
+                                      100 * MS_PER_SEC);
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    // (200px + 300px) * 0.5
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 250, 0)',
+      'Composed transform value should be composed onto the value of ' +
+      'lower-priority animation with fill:forwards during positive endDelay');
+  });
+}, 'Transform value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto a underlying animation with fill:forwards during positive ' +
+   'endDelay');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+    div.animate({ transform: 'translateX(200px)' },
+                { duration: 100 * MS_PER_SEC, delay: 50 * MS_PER_SEC });
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(100 * MS_PER_SEC);
+
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 150, 0)',
+      'Transform value for animation with positive delay should be composed ' +
+      'onto the base style');
+  });
+}, 'Transform value for animation with no keyframe at offset 0 and with ' +
+   'positive delay');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t, { style: 'transform: translateX(100px)' });
+
+    div.animate([{ offset: 0, transform: 'translateX(200px)'}],
+                { duration: 100 * MS_PER_SEC,
+                  iterationStart: 1,
+                  iterationComposite: 'accumulate' });
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 300, 0)',
+      'Transform value for animation with no keyframe at offset 1 and its ' +
+      'iterationComposite is accumulate');
+  });
+}, 'Transform value for animation with no keyframe at offset 1 and its ' +
+   'iterationComposite is accumulate');
+
+promise_test(t => {
+  var div;
+  return useTestRefreshMode(t).then(() => {
+    div = addDiv(t);
+    var lowerAnimation =
+      div.animate({ transform: [ 'translateX(100px)', 'translateX(200px)' ] },
+                  100 * MS_PER_SEC);
+    var higherAnimation = div.animate({ transform: 'translateX(300px)' },
+                                      100 * MS_PER_SEC);
+
+    lowerAnimation.timeline = null;
+    // Set current time at 50% duration.
+    lowerAnimation.currentTime = 50 * MS_PER_SEC;
+
+    return waitForPaintsFlushed();
+  }).then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(50 * MS_PER_SEC);
+
+    var transform =
+      SpecialPowers.DOMWindowUtils.getOMTAStyle(div, 'transform');
+    // (150px + 300px) * (50 * MS_PER_SEC / 100 * MS_PER_SEC) = 225px.
+    assert_matrix_equals(transform, 'matrix(1, 0, 0, 1, 225, 0)',
+      'Composed transform value should be composed onto the value of ' +
+      'lower-priority animation without timeline');
+  });
+}, 'Transform value for animation with no keyframe at offset 0 at 50% when ' +
+   'composed onto an animation without timeline');
+
+</script>
+</body>
diff --git a/dom/animation/test/style/test_missing-keyframe.html b/dom/animation/test/style/test_missing-keyframe.html
new file mode 100644
index 0000000000..4047e62408
--- /dev/null
+++ b/dom/animation/test/style/test_missing-keyframe.html
@@ -0,0 +1,110 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../testcommon.js"></script>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+test(t => {
+  var div = addDiv(t, { style: 'margin-left: 100px' });
+  div.animate([{ marginLeft: '200px' }], 100 * MS_PER_SEC);
+
+  assert_equals(getComputedStyle(div).marginLeft, '100px',
+                'The initial margin-left value should be the base value');
+}, 'Initial margin-left value for an animation with no keyframe at offset 0');
+
+test(t => {
+  var div = addDiv(t, { style: 'margin-left: 100px' });
+  div.animate([{ offset: 0, marginLeft: '200px' },
+               { offset: 1, marginLeft: '300px' }],
+              100 * MS_PER_SEC);
+  div.animate([{ marginLeft: '200px' }], 100 * MS_PER_SEC);
+
+  assert_equals(getComputedStyle(div).marginLeft, '200px',
+                'The initial margin-left value should be the initial value ' +
+                'of lower-priority animation');
+}, 'Initial margin-left value for an animation with no keyframe at offset 0 ' +
+   'is that of lower-priority animations');
+
+test(t => {
+  var div = addDiv(t, { style: 'margin-left: 100px;' +
+                               'transition: margin-left 100s -50s linear'});
+  flushComputedStyle(div);
+
+  div.style.marginLeft = '200px';
+  flushComputedStyle(div);
+
+  div.animate([{ marginLeft: '300px' }], 100 * MS_PER_SEC);
+
+  assert_equals(getComputedStyle(div).marginLeft, '150px',
+                'The initial margin-left value should be the initial value ' +
+                'of the transition');
+}, 'Initial margin-left value for an animation with no keyframe at offset 0 ' +
+   'is that of transition');
+
+test(t => {
+  var div = addDiv(t, { style: 'margin-left: 100px' });
+  var animation = div.animate([{ offset: 0, marginLeft: '200px' }],
+                              100 * MS_PER_SEC);
+
+  animation.currentTime = 50 * MS_PER_SEC;
+  assert_equals(getComputedStyle(div).marginLeft, '150px',
+                'The margin-left value at 50% should be the base value');
+}, 'margin-left value at 50% for an animation with no keyframe at offset 1');
+
+test(t => {
+  var div = addDiv(t, { style: 'margin-left: 100px' });
+  var lowerAnimation = div.animate([{ offset: 0, marginLeft: '200px' },
+                                    { offset: 1, marginLeft: '300px' }],
+                                   100 * MS_PER_SEC);
+  var higherAnimation = div.animate([{ offset: 0, marginLeft: '400px' }],
+                                    100 * MS_PER_SEC);
+
+  lowerAnimation.currentTime = 50 * MS_PER_SEC;
+  higherAnimation.currentTime = 50 * MS_PER_SEC;
+                                                 // (250px + 400px) * 0.5
+  assert_equals(getComputedStyle(div).marginLeft, '325px',
+                'The margin-left value at 50% should be additive value of ' +
+                'lower-priority animation and higher-priority animation');
+}, 'margin-left value at 50% for an animation with no keyframe at offset 1 ' +
+   'is that of lower-priority animations');
+
+test(t => {
+  var div = addDiv(t, { style: 'margin-left: 100px;' +
+                               'transition: margin-left 100s linear' });
+  flushComputedStyle(div);
+
+  div.style.marginLeft = '300px';
+  flushComputedStyle(div);
+
+  div.animate([{ offset: 0, marginLeft: '200px' }], 100 * MS_PER_SEC);
+
+  div.getAnimations().forEach(animation => {
+    animation.currentTime = 50 * MS_PER_SEC;
+  });
+                                                 // (200px + 200px) * 0.5
+  assert_equals(getComputedStyle(div).marginLeft, '200px',
+                'The margin-left value at 50% should be additive value of ' +
+                'the transition and animation');
+}, 'margin-left value at 50% for an animation with no keyframe at offset 1 ' +
+   'is that of transition');
+
+test(t => {
+  var div = addDiv(t, { style: 'margin-left: 100px' });
+
+  var animation = div.animate([{ offset: 0, marginLeft: '200px' }],
+                              { duration: 100 * MS_PER_SEC,
+                                iterationStart: 1,
+                                iterationComposite: 'accumulate' });
+
+  assert_equals(getComputedStyle(div).marginLeft, '300px',
+                'The margin-left value should be additive value of the ' +
+                'accumulation of the initial value onto the base value ');
+}, 'margin-left value for an animation with no keyframe at offset 1 and its ' +
+   'iterationComposite is accumulate');
+
+</script>
+</body>
diff --git a/dom/animation/test/style/test_transform-non-normalizable-rotate3d.html b/dom/animation/test/style/test_transform-non-normalizable-rotate3d.html
new file mode 100644
index 0000000000..ad2584ac40
--- /dev/null
+++ b/dom/animation/test/style/test_transform-non-normalizable-rotate3d.html
@@ -0,0 +1,28 @@
+<!doctype html>
+<meta charset=utf-8>
+<script src='/resources/testharness.js'></script>
+<script src='/resources/testharnessreport.js'></script>
+<script src='../testcommon.js'></script>
+<div id='log'></div>
+<script type='text/javascript'>
+'use strict';
+
+test(function(t) {
+  var target = addDiv(t);
+  target.style.transform = 'rotate3d(0, 0, 1, 90deg)';
+  target.style.transition = 'all 10s linear -5s';
+  getComputedStyle(target).transform;
+
+  target.style.transform = 'rotate3d(0, 0, 0, 270deg)';
+  var interpolated_matrix = 'matrix(' + Math.cos(Math.PI / 4) + ',' +
+                                        Math.sin(Math.PI / 4) + ',' +
+                                       -Math.sin(Math.PI / 4) + ',' +
+                                        Math.cos(Math.PI / 4) + ',' +
+                                        '0, 0)';
+  assert_matrix_equals(getComputedStyle(target).transform, interpolated_matrix,
+                       'transition from a normal rotate3d to a ' +
+                       'non-normalizable rotate3d');
+}, 'Test interpolation on non-normalizable rotate3d function');
+
+</script>
+</html>
diff --git a/dom/animation/test/testcommon.js b/dom/animation/test/testcommon.js
new file mode 100644
index 0000000000..e1645d4a19
--- /dev/null
+++ b/dom/animation/test/testcommon.js
@@ -0,0 +1,527 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Use this variable if you specify duration or some other properties
+ * for script animation.
+ * E.g., div.animate({ opacity: [0, 1] }, 100 * MS_PER_SEC);
+ *
+ * NOTE: Creating animations with short duration may cause intermittent
+ * failures in asynchronous test. For example, the short duration animation
+ * might be finished when animation.ready has been fulfilled because of slow
+ * platforms or busyness of the main thread.
+ * Setting short duration to cancel its animation does not matter but
+ * if you don't want to cancel the animation, consider using longer duration.
+ */
+const MS_PER_SEC = 1000;
+
+/* The recommended minimum precision to use for time values[1].
+ *
+ * [1] https://drafts.csswg.org/web-animations/#precision-of-time-values
+ */
+var TIME_PRECISION = 0.0005; // ms
+
+/*
+ * Allow implementations to substitute an alternative method for comparing
+ * times based on their precision requirements.
+ */
+function assert_times_equal(actual, expected, description) {
+  assert_approx_equals(actual, expected, TIME_PRECISION * 2, description);
+}
+
+/*
+ * Compare a time value based on its precision requirements with a fixed value.
+ */
+function assert_time_equals_literal(actual, expected, description) {
+  assert_approx_equals(actual, expected, TIME_PRECISION, description);
+}
+
+/*
+ * Compare matrix string like 'matrix(1, 0, 0, 1, 100, 0)'.
+ * This function allows error, 0.01, because on Android when we are scaling down
+ * the document, it results in some errors.
+ */
+function assert_matrix_equals(actual, expected, description) {
+  var matrixRegExp = /^matrix\((.+),(.+),(.+),(.+),(.+),(.+)\)/;
+  assert_regexp_match(actual, matrixRegExp, "Actual value should be a matrix");
+  assert_regexp_match(
+    expected,
+    matrixRegExp,
+    "Expected value should be a matrix"
+  );
+
+  var actualMatrixArray = actual.match(matrixRegExp).slice(1).map(Number);
+  var expectedMatrixArray = expected.match(matrixRegExp).slice(1).map(Number);
+
+  assert_equals(
+    actualMatrixArray.length,
+    expectedMatrixArray.length,
+    "Array lengths should be equal (got '" +
+      expected +
+      "' and '" +
+      actual +
+      "'): " +
+      description
+  );
+  for (var i = 0; i < actualMatrixArray.length; i++) {
+    assert_approx_equals(
+      actualMatrixArray[i],
+      expectedMatrixArray[i],
+      0.01,
+      "Matrix array should be equal (got '" +
+        expected +
+        "' and '" +
+        actual +
+        "'): " +
+        description
+    );
+  }
+}
+
+/**
+ * Compare given values which are same format of
+ * KeyframeEffectReadonly::GetProperties.
+ */
+function assert_properties_equal(actual, expected) {
+  assert_equals(actual.length, expected.length);
+
+  const compareProperties = (a, b) =>
+    a.property == b.property ? 0 : a.property < b.property ? -1 : 1;
+
+  const sortedActual = actual.sort(compareProperties);
+  const sortedExpected = expected.sort(compareProperties);
+
+  const serializeValues = values =>
+    values
+      .map(
+        value =>
+          "{ " +
+          ["offset", "value", "easing", "composite"]
+            .map(member => `${member}: ${value[member]}`)
+            .join(", ") +
+          " }"
+      )
+      .join(", ");
+
+  for (let i = 0; i < sortedActual.length; i++) {
+    assert_equals(
+      sortedActual[i].property,
+      sortedExpected[i].property,
+      "CSS property name should match"
+    );
+    assert_equals(
+      serializeValues(sortedActual[i].values),
+      serializeValues(sortedExpected[i].values),
+      `Values arrays do not match for ` + `${sortedActual[i].property} property`
+    );
+  }
+}
+
+/**
+ * Construct a object which is same to a value of
+ * KeyframeEffectReadonly::GetProperties().
+ * The method returns undefined as a value in case of missing keyframe.
+ * Therefor, we can use undefined for |value| and |easing| parameter.
+ * @param offset - keyframe offset. e.g. 0.1
+ * @param value - any keyframe value. e.g. undefined '1px', 'center', 0.5
+ * @param composite - 'replace', 'add', 'accumulate'
+ * @param easing - e.g. undefined, 'linear', 'ease' and so on
+ * @return Object -
+ *   e.g. { offset: 0.1, value: '1px', composite: 'replace', easing: 'ease'}
+ */
+function valueFormat(offset, value, composite, easing) {
+  return { offset, value, easing, composite };
+}
+
+/**
+ * Appends a div to the document body and creates an animation on the div.
+ * NOTE: This function asserts when trying to create animations with durations
+ * shorter than 100s because the shorter duration may cause intermittent
+ * failures.  If you are not sure how long it is suitable, use 100s; it's
+ * long enough but shorter than our test framework timeout (330s).
+ * If you really need to use shorter durations, use animate() function directly.
+ *
+ * @param t  The testharness.js Test object. If provided, this will be used
+ *           to register a cleanup callback to remove the div when the test
+ *           finishes.
+ * @param attrs  A dictionary object with attribute names and values to set on
+ *               the div.
+ * @param frames  The keyframes passed to Element.animate().
+ * @param options  The options passed to Element.animate().
+ */
+function addDivAndAnimate(t, attrs, frames, options) {
+  let animDur = typeof options === "object" ? options.duration : options;
+  assert_greater_than_equal(
+    animDur,
+    100 * MS_PER_SEC,
+    "Clients of this addDivAndAnimate API must request a duration " +
+      "of at least 100s, to avoid intermittent failures from e.g." +
+      "the main thread being busy for an extended period"
+  );
+
+  return addDiv(t, attrs).animate(frames, options);
+}
+
+/**
+ * Appends a div to the document body.
+ *
+ * @param t  The testharness.js Test object. If provided, this will be used
+ *           to register a cleanup callback to remove the div when the test
+ *           finishes.
+ *
+ * @param attrs  A dictionary object with attribute names and values to set on
+ *               the div.
+ */
+function addDiv(t, attrs) {
+  var div = document.createElement("div");
+  if (attrs) {
+    for (var attrName in attrs) {
+      div.setAttribute(attrName, attrs[attrName]);
+    }
+  }
+  document.body.appendChild(div);
+  if (t && typeof t.add_cleanup === "function") {
+    t.add_cleanup(function () {
+      if (div.parentNode) {
+        div.remove();
+      }
+    });
+  }
+  return div;
+}
+
+/**
+ * Appends a style div to the document head.
+ *
+ * @param t  The testharness.js Test object. If provided, this will be used
+ *           to register a cleanup callback to remove the style element
+ *           when the test finishes.
+ *
+ * @param rules  A dictionary object with selector names and rules to set on
+ *               the style sheet.
+ */
+function addStyle(t, rules) {
+  var extraStyle = document.createElement("style");
+  document.head.appendChild(extraStyle);
+  if (rules) {
+    var sheet = extraStyle.sheet;
+    for (var selector in rules) {
+      sheet.insertRule(
+        selector + "{" + rules[selector] + "}",
+        sheet.cssRules.length
+      );
+    }
+  }
+
+  if (t && typeof t.add_cleanup === "function") {
+    t.add_cleanup(function () {
+      extraStyle.remove();
+    });
+  }
+}
+
+/**
+ * Takes a CSS property (e.g. margin-left) and returns the equivalent IDL
+ * name (e.g. marginLeft).
+ */
+function propertyToIDL(property) {
+  var prefixMatch = property.match(/^-(\w+)-/);
+  if (prefixMatch) {
+    var prefix = prefixMatch[1] === "moz" ? "Moz" : prefixMatch[1];
+    property = prefix + property.substring(prefixMatch[0].length - 1);
+  }
+  // https://drafts.csswg.org/cssom/#css-property-to-idl-attribute
+  return property.replace(/-([a-z])/gi, function (str, group) {
+    return group.toUpperCase();
+  });
+}
+
+/**
+ * Promise wrapper for requestAnimationFrame.
+ */
+function waitForFrame() {
+  return new Promise(function (resolve, reject) {
+    window.requestAnimationFrame(resolve);
+  });
+}
+
+/**
+ * Waits for a requestAnimationFrame callback in the next refresh driver tick.
+ * Note that the 'dom.animations-api.core.enabled' and
+ * 'dom.animations-api.timelines.enabled' prefs should be true to use this
+ * function.
+ */
+function waitForNextFrame(aWindow = window) {
+  const timeAtStart = aWindow.document.timeline.currentTime;
+  return new Promise(resolve => {
+    aWindow.requestAnimationFrame(() => {
+      if (timeAtStart === aWindow.document.timeline.currentTime) {
+        aWindow.requestAnimationFrame(resolve);
+      } else {
+        resolve();
+      }
+    });
+  });
+}
+
+/**
+ * Returns a Promise that is resolved after the given number of consecutive
+ * animation frames have occured (using requestAnimationFrame callbacks).
+ *
+ * @param aFrameCount  The number of animation frames.
+ * @param aOnFrame  An optional function to be processed in each animation frame.
+ * @param aWindow  An optional window object to be used for requestAnimationFrame.
+ */
+function waitForAnimationFrames(aFrameCount, aOnFrame, aWindow = window) {
+  const timeAtStart = aWindow.document.timeline.currentTime;
+  return new Promise(function (resolve, reject) {
+    function handleFrame() {
+      if (aOnFrame && typeof aOnFrame === "function") {
+        aOnFrame();
+      }
+      if (
+        timeAtStart != aWindow.document.timeline.currentTime &&
+        --aFrameCount <= 0
+      ) {
+        resolve();
+      } else {
+        aWindow.requestAnimationFrame(handleFrame); // wait another frame
+      }
+    }
+    aWindow.requestAnimationFrame(handleFrame);
+  });
+}
+
+/**
+ * Promise wrapper for requestIdleCallback.
+ */
+function waitForIdle() {
+  return new Promise(resolve => {
+    requestIdleCallback(resolve);
+  });
+}
+
+/**
+ * Wrapper that takes a sequence of N animations and returns:
+ *
+ *   Promise.all([animations[0].ready, animations[1].ready, ... animations[N-1].ready]);
+ */
+function waitForAllAnimations(animations) {
+  return Promise.all(
+    animations.map(function (animation) {
+      return animation.ready;
+    })
+  );
+}
+
+/**
+ * Flush the computed style for the given element. This is useful, for example,
+ * when we are testing a transition and need the initial value of a property
+ * to be computed so that when we synchronouslyet set it to a different value
+ * we actually get a transition instead of that being the initial value.
+ */
+function flushComputedStyle(elem) {
+  var cs = getComputedStyle(elem);
+  cs.marginLeft;
+}
+
+if (opener) {
+  for (var funcName of [
+    "async_test",
+    "assert_not_equals",
+    "assert_equals",
+    "assert_approx_equals",
+    "assert_less_than",
+    "assert_less_than_equal",
+    "assert_greater_than",
+    "assert_between_inclusive",
+    "assert_true",
+    "assert_false",
+    "assert_class_string",
+    "assert_throws",
+    "assert_unreached",
+    "assert_regexp_match",
+    "promise_test",
+    "test",
+  ]) {
+    if (opener[funcName]) {
+      window[funcName] = opener[funcName].bind(opener);
+    }
+  }
+
+  window.EventWatcher = opener.EventWatcher;
+
+  function done() {
+    opener.add_completion_callback(function () {
+      self.close();
+    });
+    opener.done();
+  }
+}
+
+/*
+ * Returns a promise that is resolved when the document has finished loading.
+ */
+function waitForDocumentLoad() {
+  return new Promise(function (resolve, reject) {
+    if (document.readyState === "complete") {
+      resolve();
+    } else {
+      window.addEventListener("load", resolve);
+    }
+  });
+}
+
+/*
+ * Enters test refresh mode, and restores the mode when |t| finishes.
+ */
+function useTestRefreshMode(t) {
+  function ensureNoSuppressedPaints() {
+    return new Promise(resolve => {
+      function checkSuppressedPaints() {
+        if (!SpecialPowers.DOMWindowUtils.paintingSuppressed) {
+          resolve();
+        } else {
+          window.requestAnimationFrame(checkSuppressedPaints);
+        }
+      }
+      checkSuppressedPaints();
+    });
+  }
+
+  return ensureNoSuppressedPaints().then(() => {
+    SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(0);
+    t.add_cleanup(() => {
+      SpecialPowers.DOMWindowUtils.restoreNormalRefresh();
+    });
+  });
+}
+
+/**
+ * Returns true if off-main-thread animations.
+ */
+function isOMTAEnabled() {
+  const OMTAPrefKey = "layers.offmainthreadcomposition.async-animations";
+  return (
+    SpecialPowers.DOMWindowUtils.layerManagerRemote &&
+    SpecialPowers.getBoolPref(OMTAPrefKey)
+  );
+}
+
+/**
+ * Append an SVG element to the target element.
+ *
+ * @param target The element which want to append.
+ * @param attrs  A array object with attribute name and values to set on
+ *               the SVG element.
+ * @return An SVG outer element.
+ */
+function addSVGElement(target, tag, attrs) {
+  if (!target) {
+    return null;
+  }
+  var element = document.createElementNS("http://www.w3.org/2000/svg", tag);
+  if (attrs) {
+    for (var attrName in attrs) {
+      element.setAttributeNS(null, attrName, attrs[attrName]);
+    }
+  }
+  target.appendChild(element);
+  return element;
+}
+
+/*
+ * Get Animation distance between two specified values for a specific property.
+ *
+ * @param target The target element.
+ * @param prop The CSS property.
+ * @param v1 The first property value.
+ * @param v2 The Second property value.
+ *
+ * @return The distance between |v1| and |v2| for |prop| on |target|.
+ */
+function getDistance(target, prop, v1, v2) {
+  if (!target) {
+    return 0.0;
+  }
+  return SpecialPowers.DOMWindowUtils.computeAnimationDistance(
+    target,
+    prop,
+    v1,
+    v2
+  );
+}
+
+/*
+ * A promise wrapper for waiting MozAfterPaint.
+ */
+function waitForPaints() {
+  // FIXME: Bug 1415065. Instead waiting for two requestAnimationFrames, we
+  // should wait for MozAfterPaint once after MozAfterPaint is fired properly
+  // (bug 1341294).
+  return waitForAnimationFrames(2);
+}
+
+// Returns true if |aAnimation| begins at the current timeline time.  We
+// sometimes need to detect this case because if we started an animation
+// asynchronously (e.g. using play()) and then ended up running the next frame
+// at precisely the time the animation started (due to aligning with vsync
+// refresh rate) then we won't end up restyling in that frame.
+function animationStartsRightNow(aAnimation) {
+  return (
+    aAnimation.startTime === aAnimation.timeline.currentTime &&
+    aAnimation.currentTime === 0
+  );
+}
+
+// Waits for a given animation being ready to restyle.
+async function waitForAnimationReadyToRestyle(aAnimation) {
+  await aAnimation.ready;
+  // If |aAnimation| begins at the current timeline time, we will not process
+  // restyling in the initial frame because of aligning with the refresh driver,
+  // the animation frame in which the ready promise is resolved happens to
+  // coincide perfectly with the start time of the animation.  In this case no
+  // restyling is needed in the frame so we have to wait one more frame.
+  if (animationStartsRightNow(aAnimation)) {
+    await waitForNextFrame(aAnimation.ownerGlobal);
+  }
+}
+
+function getDocShellForObservingRestylesForWindow(aWindow) {
+  const docShell = SpecialPowers.wrap(aWindow).docShell;
+
+  docShell.recordProfileTimelineMarkers = true;
+  docShell.popProfileTimelineMarkers();
+
+  return docShell;
+}
+
+// Returns the animation restyle markers observed during |frameCount| refresh
+// driver ticks in this `window`.  This function is typically used to count the
+// number of restyles that take place as part of the style update that happens
+// on each refresh driver tick, as opposed to synchronous restyles triggered by
+// script.
+//
+// For the latter observeAnimSyncStyling (below) should be used.
+function observeStyling(frameCount, onFrame) {
+  return observeStylingInTargetWindow(window, frameCount, onFrame);
+}
+
+// As with observeStyling but applied to target window |aWindow|.
+function observeStylingInTargetWindow(aWindow, aFrameCount, aOnFrame) {
+  const docShell = getDocShellForObservingRestylesForWindow(aWindow);
+
+  return new Promise(resolve => {
+    return waitForAnimationFrames(aFrameCount, aOnFrame, aWindow).then(() => {
+      const markers = docShell.popProfileTimelineMarkers();
+      docShell.recordProfileTimelineMarkers = false;
+      const stylingMarkers = Array.prototype.filter.call(
+        markers,
+        (marker, index) => {
+          return marker.name == "Styles" && marker.isAnimationOnly;
+        }
+      );
+      resolve(stylingMarkers);
+    });
+  });
+}
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