--- a/testing/web-platform/tests/web-animations/animation-effect-timing/duration.html
+++ b/testing/web-platform/tests/web-animations/animation-effect-timing/duration.html
@@ -10,21 +10,20 @@
 <div id="log"></div>
 <script>
 'use strict';
 
 test(function(t) {
   var div = createDiv(t);
   var anim = div.animate({ opacity: [ 0, 1 ] }, 2000);
   anim.effect.timing.duration = 123.45;
-  assert_approx_equals(anim.effect.timing.duration, 123.45, 0.000001,
-                       'set duration 123.45');
-  assert_approx_equals(anim.effect.getComputedTiming().duration, 123.45,
-                       0.000001,
-                       'getComputedTiming() after set duration 123.45');
+  assert_times_equal(anim.effect.timing.duration, 123.45,
+                     'set duration 123.45');
+  assert_times_equal(anim.effect.getComputedTiming().duration, 123.45,
+                     'getComputedTiming() after set duration 123.45');
 }, 'set duration 123.45');
 
 test(function(t) {
   var div = createDiv(t);
   var anim = div.animate({ opacity: [ 0, 1 ] }, 2000);
   anim.effect.timing.duration = 'auto';
   assert_equals(anim.effect.timing.duration, 'auto', 'set duration \'auto\'');
   assert_equals(anim.effect.getComputedTiming().duration, 0,

--- a/testing/web-platform/tests/web-animations/animation-effect-timing/endDelay.html
+++ b/testing/web-platform/tests/web-animations/animation-effect-timing/endDelay.html
@@ -10,21 +10,20 @@
 <div id="log"></div>
 <script>
 'use strict';
 
 test(function(t) {
   var div = createDiv(t);
   var anim = div.animate({ opacity: [ 0, 1 ] }, 2000);
   anim.effect.timing.endDelay = 123.45;
-  assert_approx_equals(anim.effect.timing.endDelay, 123.45, 0.000001,
-                       'set endDelay 123.45');
-  assert_approx_equals(anim.effect.getComputedTiming().endDelay, 123.45,
-                       0.000001,
-                       'getComputedTiming() after set endDelay 123.45');
+  assert_times_equal(anim.effect.timing.endDelay, 123.45,
+                     'set endDelay 123.45');
+  assert_times_equal(anim.effect.getComputedTiming().endDelay, 123.45,
+                     'getComputedTiming() after set endDelay 123.45');
 }, 'set endDelay 123.45');
 
 test(function(t) {
   var div = createDiv(t);
   var anim = div.animate({ opacity: [ 0, 1 ] }, 2000);
   anim.effect.timing.endDelay = -1000;
   assert_equals(anim.effect.timing.endDelay, -1000, 'set endDelay -1000');
   assert_equals(anim.effect.getComputedTiming().endDelay, -1000,

--- a/testing/web-platform/tests/web-animations/animation/finish.html
+++ b/testing/web-platform/tests/web-animations/animation/finish.html
@@ -91,42 +91,40 @@ promise_test(function(t) {
   var animation = div.animate(gKeyFrames, 100 * MS_PER_SEC);
   animation.pause();
   return animation.ready.then(function() {
     animation.finish();
 
     assert_equals(animation.playState, 'finished',
                   'The play state of a paused animation should become ' +
                   '"finished" after finish() is called');
-    assert_approx_equals(animation.startTime,
-                         animation.timeline.currentTime - 100 * MS_PER_SEC,
-                         0.0001,
-                         'The start time of a paused animation should be set ' +
-                         'after calling finish()');
+    assert_times_equal(animation.startTime,
+                       animation.timeline.currentTime - 100 * MS_PER_SEC,
+                       'The start time of a paused animation should be set ' +
+                       'after calling finish()');
   });
 }, 'Test finish() while paused');
 
 test(function(t) {
   var div = createDiv(t);
   var animation = div.animate(gKeyFrames, 100 * MS_PER_SEC);
   animation.pause();
   // Update playbackRate so we can test that the calculated startTime
   // respects it
   animation.playbackRate = 2;
   // While animation is still pause-pending call finish()
   animation.finish();
 
   assert_equals(animation.playState, 'finished',
                 'The play state of a pause-pending animation should become ' +
                 '"finished" after finish() is called');
-  assert_approx_equals(animation.startTime,
-                       animation.timeline.currentTime - 100 * MS_PER_SEC / 2,
-                       0.0001,
-                       'The start time of a pause-pending animation should ' +
-                       'be set after calling finish()');
+  assert_times_equal(animation.startTime,
+                     animation.timeline.currentTime - 100 * MS_PER_SEC / 2,
+                     'The start time of a pause-pending animation should ' +
+                     'be set after calling finish()');
 }, 'Test finish() while pause-pending with positive playbackRate');
 
 test(function(t) {
   var div = createDiv(t);
   var animation = div.animate(gKeyFrames, 100 * MS_PER_SEC);
   animation.pause();
   animation.playbackRate = -2;
   animation.finish();
@@ -143,21 +141,20 @@ test(function(t) {
   var div = createDiv(t);
   var animation = div.animate(gKeyFrames, 100 * MS_PER_SEC);
   animation.playbackRate = 0.5;
   animation.finish();
 
   assert_equals(animation.playState, 'finished',
                 'The play state of a play-pending animation should become ' +
                 '"finished" after finish() is called');
-  assert_approx_equals(animation.startTime,
-                       animation.timeline.currentTime - 100 * MS_PER_SEC / 0.5,
-                       0.0001,
-                       'The start time of a play-pending animation should ' +
-                       'be set after calling finish()');
+  assert_times_equal(animation.startTime,
+                     animation.timeline.currentTime - 100 * MS_PER_SEC / 0.5,
+                     'The start time of a play-pending animation should ' +
+                     'be set after calling finish()');
 }, 'Test finish() while play-pending');
 
 // FIXME: Add a test for when we are play-pending without an active timeline.
 // - In that case even after calling finish() we should still be pending but
 //   the current time should be updated
 
 promise_test(function(t) {
   var div = createDiv(t);

--- a/testing/web-platform/tests/web-animations/testcommon.js
+++ b/testing/web-platform/tests/web-animations/testcommon.js
@@ -3,19 +3,33 @@ Distributed under both the W3C Test Suit
 3-clause BSD License [2]. To contribute to a W3C Test Suite, see the
 policies and contribution forms [3].
 
 [1] http://www.w3.org/Consortium/Legal/2008/04-testsuite-license
 [2] http://www.w3.org/Consortium/Legal/2008/03-bsd-license
 [3] http://www.w3.org/2004/10/27-testcases
  */
 
-"use strict";
+'use strict';
+
 var MS_PER_SEC = 1000;
 
+// The recommended minimum precision to use for time values[1].
+//
+// [1] https://w3c.github.io/web-animations/#precision-of-time-values
+var TIME_PRECISION = 0.000001;
+
+// Allow implementations to substitute an alternative method for comparing
+// times based on their precision requirements.
+if (!window.assert_times_equal) {
+  window.assert_times_equal = function(actual, expected, description) {
+    assert_approx_equals(actual, expected, TIME_PRECISION, description);
+  }
+}
+
 // creates div element, appends it to the document body and
 // removes the created element during test cleanup
 function createDiv(test, doc) {
   if (!doc) {
     doc = document;
   }
   var div = doc.createElement('div');
   doc.body.appendChild(div);