--- a/js/src/devtools/rootAnalysis/analyzeHeapWrites.js
+++ b/js/src/devtools/rootAnalysis/analyzeHeapWrites.js
@@ -385,16 +385,17 @@ function ignoreContents(entry)
         "Gecko_NewStyleQuoteValues",
         "Gecko_NewCSSValueSharedList",
         "Gecko_NewNoneTransform",
         "Gecko_NewGridTemplateAreasValue",
         /nsCSSValue::SetCalcValue/,
         /CSSValueSerializeCalcOps::Append/,
         "Gecko_CSSValue_SetFunction",
         "Gecko_CSSValue_SetArray",
+        "Gecko_CSSValue_InitSharedList",
         "Gecko_EnsureMozBorderColors",
         "Gecko_ClearMozBorderColors",
         "Gecko_AppendMozBorderColors",
         "Gecko_CopyMozBorderColors",
         "Gecko_SetNullImageValue",
 
         // Needs main thread assertions or other fixes.
         /UndisplayedMap::GetEntryFor/,

--- a/layout/style/ServoBindings.cpp
+++ b/layout/style/ServoBindings.cpp
@@ -2027,16 +2027,31 @@ Gecko_CSSValue_SetPairList(nsCSSValueBor
   MOZ_ASSERT(NS_IsMainThread());
   nsCSSValuePairList* item = aCSSValue->SetPairListValue();
   for (uint32_t i = 1; i < aLen; ++i) {
     item->mNext = new nsCSSValuePairList;
     item = item->mNext;
   }
 }
 
+void
+Gecko_CSSValue_InitSharedList(nsCSSValueBorrowedMut aCSSValue,
+                              uint32_t aLen)
+{
+  MOZ_ASSERT(aLen > 0, "Must create at least one nsCSSValueList (mHead)");
+
+  nsCSSValueSharedList* list = new nsCSSValueSharedList;
+  aCSSValue->SetSharedListValue(list);
+  list->mHead = new nsCSSValueList;
+  nsCSSValueList* cur = list->mHead;
+  for (uint32_t i = 1; i < aLen; ++i) {
+    cur->mNext = new nsCSSValueList;
+    cur = cur->mNext;
+  }
+}
 
 bool
 Gecko_PropertyId_IsPrefEnabled(nsCSSPropertyID id)
 {
   return nsCSSProps::IsEnabled(id);
 }
 
 void

--- a/layout/style/ServoBindings.h
+++ b/layout/style/ServoBindings.h
@@ -503,16 +503,17 @@ void Gecko_CSSValue_SetStringFromAtom(ns
 void Gecko_CSSValue_SetAtomIdent(nsCSSValueBorrowedMut css_value, nsIAtom* atom);
 void Gecko_CSSValue_SetArray(nsCSSValueBorrowedMut css_value, int32_t len);
 void Gecko_CSSValue_SetURL(nsCSSValueBorrowedMut css_value, ServoBundledURI uri);
 void Gecko_CSSValue_SetInt(nsCSSValueBorrowedMut css_value, int32_t integer, nsCSSUnit unit);
 void Gecko_CSSValue_SetPair(nsCSSValueBorrowedMut css_value,
                             nsCSSValueBorrowed xvalue, nsCSSValueBorrowed yvalue);
 void Gecko_CSSValue_SetList(nsCSSValueBorrowedMut css_value, uint32_t len);
 void Gecko_CSSValue_SetPairList(nsCSSValueBorrowedMut css_value, uint32_t len);
+void Gecko_CSSValue_InitSharedList(nsCSSValueBorrowedMut css_value, uint32_t len);
 void Gecko_CSSValue_Drop(nsCSSValueBorrowedMut css_value);
 NS_DECL_THREADSAFE_FFI_REFCOUNTING(nsCSSValueSharedList, CSSValueSharedList);
 bool Gecko_PropertyId_IsPrefEnabled(nsCSSPropertyID id);
 
 void Gecko_nsStyleFont_SetLang(nsStyleFont* font, nsIAtom* atom);
 void Gecko_nsStyleFont_CopyLangFrom(nsStyleFont* aFont, const nsStyleFont* aSource);
 void Gecko_nsStyleFont_FixupNoneGeneric(nsStyleFont* font,
                                         RawGeckoPresContextBorrowed pres_context);

--- a/layout/style/nsStyleTransformMatrix.cpp
+++ b/layout/style/nsStyleTransformMatrix.cpp
@@ -435,33 +435,53 @@ ProcessMatrixOperator(Matrix4x4& aMatrix
                       nsStyleContext* aContext,
                       nsPresContext* aPresContext,
                       RuleNodeCacheConditions& aConditions,
                       TransformReferenceBox& aRefBox,
                       bool* aContains3dTransform)
 {
   NS_PRECONDITION(aData->Count() == 4, "Invalid array!");
 
-  Matrix4x4 matrix1, matrix2;
-  if (aData->Item(1).GetUnit() == eCSSUnit_List) {
-    matrix1 = nsStyleTransformMatrix::ReadTransforms(aData->Item(1).GetListValue(),
-                             aContext, aPresContext,
-                             aConditions,
-                             aRefBox, nsPresContext::AppUnitsPerCSSPixel(),
-                             aContains3dTransform);
-  }
-  if (aData->Item(2).GetUnit() == eCSSUnit_List) {
-    matrix2 = ReadTransforms(aData->Item(2).GetListValue(),
-                             aContext, aPresContext,
-                             aConditions,
-                             aRefBox, nsPresContext::AppUnitsPerCSSPixel(),
-                             aContains3dTransform);
-  }
+  auto readTransform = [&](const nsCSSValue& aValue) -> Matrix4x4 {
+    const nsCSSValueList* list = nullptr;
+    switch (aValue.GetUnit()) {
+      case eCSSUnit_List:
+        // For Gecko style backend.
+        list = aValue.GetListValue();
+        break;
+      case eCSSUnit_SharedList:
+        // For Servo style backend. The transform lists of interpolatematrix
+        // are not created on the main thread (i.e. during parallel traversal),
+        // and nsCSSValueList_heap is not thread safe. Therefore, we use
+        // nsCSSValueSharedList as a workaround.
+        list = aValue.GetSharedListValue()->mHead;
+        break;
+      default:
+        list = nullptr;
+    }
+
+    Matrix4x4 matrix;
+    if (!list) {
+      return matrix;
+    }
+
+    float appUnitPerCSSPixel = nsPresContext::AppUnitsPerCSSPixel();
+    matrix = nsStyleTransformMatrix::ReadTransforms(list,
+                                                    aContext,
+                                                    aPresContext,
+                                                    aConditions,
+                                                    aRefBox,
+                                                    appUnitPerCSSPixel,
+                                                    aContains3dTransform);
+    return matrix;
+  };
+
+  Matrix4x4 matrix1 = readTransform(aData->Item(1));
+  Matrix4x4 matrix2 = readTransform(aData->Item(2));
   double progress = aData->Item(3).GetPercentValue();
-
   aMatrix =
     OperateTransformMatrix<Operator>(matrix1, matrix2, progress) * aMatrix;
 }
 
 /* Helper function to process two matrices that we need to interpolate between */
 void
 ProcessInterpolateMatrix(Matrix4x4& aMatrix,
                          const nsCSSValue::Array* aData,