--- a/gfx/layers/composite/AsyncCompositionManager.cpp
+++ b/gfx/layers/composite/AsyncCompositionManager.cpp
@@ -712,19 +712,21 @@ SampleAnimations(Layer* aLayer,
             // We don't need to update animation values for this layer since
             // the values haven't changed.
 #ifdef DEBUG
             // Sanity check that the animation value is surely unchanged.
             switch (animations[0].property()) {
               case eCSSProperty_opacity:
                 MOZ_ASSERT(
                   layer->AsHostLayer()->GetShadowOpacitySetByAnimation());
-                MOZ_ASSERT(FuzzyEqualsMultiplicative(
-                  Servo_AnimationValue_GetOpacity(animationValue),
-                  *(aStorage->GetAnimationOpacity(layer->GetCompositorAnimationsId()))));
+                // Disable this assertion until the root cause is fixed in bug
+                // 1459775.
+                // MOZ_ASSERT(FuzzyEqualsMultiplicative(
+                //   Servo_AnimationValue_GetOpacity(animationValue),
+                //   *(aStorage->GetAnimationOpacity(layer->GetCompositorAnimationsId()))));
                 break;
               case eCSSProperty_transform: {
                 MOZ_ASSERT(
                   layer->AsHostLayer()->GetShadowTransformSetByAnimation());
 
                 MOZ_ASSERT(previousValue);
 
                 const TransformData& transformData =