--- a/dom/animation/test/chrome/test_running_on_compositor.html
+++ b/dom/animation/test/chrome/test_running_on_compositor.html
@@ -63,16 +63,27 @@ function assert_animation_is_not_running
 }
 
 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 waitForFrame();
+  }
+
   await waitForPaints();
 
   assert_animation_is_running_on_compositor(animation,
      'Animation reports that it is running on the compositor'
      + ' during playback');
 
   div.style.animationPlayState = 'paused';