--- a/layout/style/nsTransitionManager.cpp
+++ b/layout/style/nsTransitionManager.cpp
@@ -517,17 +517,17 @@ nsTransitionManager::StyleContextChanged
   }
 
   // NOTE: Things in this function (and ConsiderInitiatingTransition)
   // should never call PeekStyleData because we don't preserve gotten
   // structs across reframes.
 
   // Return sooner (before the startedAny check below) for the most
   // common case: no transitions specified or running.
-  const nsStyleDisplay *disp = newStyleContext->StyleDisplay();
+  const nsStyleDisplay* disp = newStyleContext->StyleDisplay();
   CSSPseudoElementType pseudoType = newStyleContext->GetPseudoType();
   if (pseudoType != CSSPseudoElementType::NotPseudo) {
     if (pseudoType != CSSPseudoElementType::before &&
         pseudoType != CSSPseudoElementType::after) {
       return;
     }
 
     NS_ASSERTION((pseudoType == CSSPseudoElementType::before &&
@@ -593,17 +593,17 @@ nsTransitionManager::StyleContextChanged
   }
 
   nsAutoAnimationMutationBatch mb(aElement->OwnerDoc());
 
   DebugOnly<bool> startedAny = false;
   // We don't have to update transitions if display:none, although we will
   // cancel them after restyling.
   if (!afterChangeStyle->IsInDisplayNoneSubtree()) {
-    startedAny = DoUpdateTransitions(disp,
+    startedAny = DoUpdateTransitions(*disp,
                                      aElement,
                                      afterChangeStyle->GetPseudoType(),
                                      collection,
                                      aOldStyleContext->AsGecko(),
                                      afterChangeStyle->AsGecko());
   }
 
   MOZ_ASSERT(!startedAny || collection,
@@ -642,46 +642,45 @@ nsTransitionManager::UpdateTransitions(
 {
   if (!mPresContext->IsDynamic()) {
     // For print or print preview, ignore transitions.
     return false;
   }
 
   CSSTransitionCollection* collection =
     CSSTransitionCollection::GetAnimationCollection(aElement, aPseudoType);
-  const nsStyleDisplay *disp =
+  const nsStyleDisplay* disp =
       aNewStyle->ComputedData()->GetStyleDisplay();
-  return DoUpdateTransitions(disp,
+  return DoUpdateTransitions(*disp,
                              aElement, aPseudoType,
                              collection,
                              aOldStyle, aNewStyle);
 }
 
 template<typename StyleType>
 bool
 nsTransitionManager::DoUpdateTransitions(
-  const nsStyleDisplay* aDisp,
+  const nsStyleDisplay& aDisp,
   dom::Element* aElement,
   CSSPseudoElementType aPseudoType,
   CSSTransitionCollection*& aElementTransitions,
   StyleType aOldStyle,
   StyleType aNewStyle)
 {
-  MOZ_ASSERT(aDisp, "Null nsStyleDisplay");
   MOZ_ASSERT(!aElementTransitions ||
              aElementTransitions->mElement == aElement, "Element mismatch");
 
   // Per http://lists.w3.org/Archives/Public/www-style/2009Aug/0109.html
   // I'll consider only the transitions from the number of items in
   // 'transition-property' on down, and later ones will override earlier
   // ones (tracked using |whichStarted|).
   bool startedAny = false;
   nsCSSPropertyIDSet whichStarted;
-  for (uint32_t i = aDisp->mTransitionPropertyCount; i-- != 0; ) {
-    const StyleTransition& t = aDisp->mTransitions[i];
+  for (uint32_t i = aDisp.mTransitionPropertyCount; i-- != 0; ) {
+    const StyleTransition& t = aDisp.mTransitions[i];
     // Check the combined duration (combination of delay and duration)
     // first, since it defaults to zero, which means we can ignore the
     // transition.
     if (t.GetCombinedDuration() > 0.0f) {
       // We might have something to transition.  See if any of the
       // properties in question changed and are animatable.
       // FIXME: Would be good to find a way to share code between this
       // interpretation of transition-property and the one below.
@@ -723,21 +722,21 @@ nsTransitionManager::DoUpdateTransitions
   // for properties that just changed (and are still in the set of
   // properties to transition), but for which we didn't just start the
   // transition.  This can happen delay and duration are both zero, or
   // because the new value is not interpolable.
   // Note that we also do the latter set of work in
   // nsTransitionManager::PruneCompletedTransitions.
   if (aElementTransitions) {
     bool checkProperties =
-      aDisp->mTransitions[0].GetProperty() != eCSSPropertyExtra_all_properties;
+      aDisp.mTransitions[0].GetProperty() != eCSSPropertyExtra_all_properties;
     nsCSSPropertyIDSet allTransitionProperties;
     if (checkProperties) {
-      for (uint32_t i = aDisp->mTransitionPropertyCount; i-- != 0; ) {
-        const StyleTransition& t = aDisp->mTransitions[i];
+      for (uint32_t i = aDisp.mTransitionPropertyCount; i-- != 0; ) {
+        const StyleTransition& t = aDisp.mTransitions[i];
         // FIXME: Would be good to find a way to share code between this
         // interpretation of transition-property and the one above.
         nsCSSPropertyID property = t.GetProperty();
         if (property == eCSSPropertyExtra_no_properties ||
             property == eCSSPropertyExtra_variable ||
             property == eCSSProperty_UNKNOWN) {
           // Nothing to do, but need to exclude this from cases below.
         } else if (property == eCSSPropertyExtra_all_properties) {

--- a/layout/style/nsTransitionManager.h
+++ b/layout/style/nsTransitionManager.h
@@ -425,17 +425,17 @@ protected:
     OwningCSSTransitionPtrArray;
 
   // Update transitions. This will start new transitions,
   // replace existing transitions, and stop existing transitions
   // as needed. aDisp and aElement must be non-null.
   // aElementTransitions is the collection of current transitions, and it
   // could be a nullptr if we don't have any transitions.
   template<typename StyleType> bool
-  DoUpdateTransitions(const nsStyleDisplay* aDisp,
+  DoUpdateTransitions(const nsStyleDisplay& aDisp,
                       mozilla::dom::Element* aElement,
                       mozilla::CSSPseudoElementType aPseudoType,
                       CSSTransitionCollection*& aElementTransitions,
                       StyleType aOldStyle,
                       StyleType aNewStyle);
 
   template<typename StyleType> void
   ConsiderInitiatingTransition(nsCSSPropertyID aProperty,