--- a/gfx/layers/wr/WebRenderCommandBuilder.cpp
+++ b/gfx/layers/wr/WebRenderCommandBuilder.cpp
@@ -901,17 +901,17 @@ HasActiveChildren(const nsDisplayList& a
 //
 // We can't easily use GetLayerState because it wants a bunch of layers related information.
 static bool
 IsItemProbablyActive(nsDisplayItem* aItem, nsDisplayListBuilder* aDisplayListBuilder)
 {
   switch (aItem->GetType()) {
   case DisplayItemType::TYPE_TRANSFORM: {
     nsDisplayTransform* transformItem = static_cast<nsDisplayTransform*>(aItem);
-    Matrix4x4Flagged t = transformItem->GetTransform();
+    const Matrix4x4Flagged& t = transformItem->GetTransform();
     Matrix t2d;
     bool is2D = t.Is2D(&t2d);
     GP("active: %d\n", transformItem->MayBeAnimated(aDisplayListBuilder));
     return transformItem->MayBeAnimated(aDisplayListBuilder) || !is2D || HasActiveChildren(*transformItem->GetChildren(), aDisplayListBuilder);
   }
   case DisplayItemType::TYPE_OPACITY: {
     nsDisplayOpacity* opacityItem = static_cast<nsDisplayOpacity*>(aItem);
     bool active = opacityItem->NeedsActiveLayer(aDisplayListBuilder, opacityItem->Frame());
@@ -1018,17 +1018,17 @@ Grouper::ConstructGroups(nsDisplayListBu
 
       currentGroup = &groupData->mFollowingGroup;
 
       startOfCurrentGroup = item->GetAbove();
     } else { // inactive item
 
       if (item->GetType() == DisplayItemType::TYPE_TRANSFORM) {
         nsDisplayTransform* transformItem = static_cast<nsDisplayTransform*>(item);
-        Matrix4x4Flagged t = transformItem->GetTransform();
+        const Matrix4x4Flagged& t = transformItem->GetTransform();
         Matrix t2d;
         bool is2D = t.Is2D(&t2d);
         MOZ_RELEASE_ASSERT(is2D, "Non-2D transforms should be treated as active");
 
         // Save the current transform.
         Matrix m = mTransform;
 
         GP("t2d: %f %f\n", t2d._31, t2d._32);
@@ -1065,17 +1065,17 @@ Grouper::ConstructGroupInsideInactive(We
   DIGroup* currentGroup = aGroup;
 
   nsDisplayItem* item = aList->GetBottom();
   while (item) {
     nsDisplayList* children = item->GetChildren();
 
     if (item->GetType() == DisplayItemType::TYPE_TRANSFORM) {
       nsDisplayTransform* transformItem = static_cast<nsDisplayTransform*>(item);
-      Matrix4x4Flagged t = transformItem->GetTransform();
+      const Matrix4x4Flagged& t = transformItem->GetTransform();
       Matrix t2d;
       bool is2D = t.Is2D(&t2d);
       MOZ_RELEASE_ASSERT(is2D, "Non-2D transforms should be treated as active");
 
       Matrix m = mTransform;
 
       GP("t2d: %f %f\n", t2d._31, t2d._32);
       mTransform.PreMultiply(t2d);