--- a/layout/style/nsRuleNode.h
+++ b/layout/style/nsRuleNode.h
@@ -45,19 +45,16 @@ public:
     }
   }
   bool ClearStyleData(nsStyleStructID aSID) {
     bool shouldDelete = mStyleStructs[aSID] &&
                         mStyleStructs[aSID]->ReleaseWithoutDestroying() == 0;
     mStyleStructs[aSID] = nullptr;
     return shouldDelete;
   }
-  void SwapStyleData(nsStyleStructID aSID, nsInheritedStyleData& aOther) {
-    std::swap(mStyleStructs[aSID], aOther.mStyleStructs[aSID]);
-  }
   bool ReplaceStyleData(nsStyleStructID aSID, nsStyleStruct* aStyleStruct) {
     MOZ_ASSERT(aStyleStruct);
     nsStyleStruct* old = mStyleStructs[aSID];
     aStyleStruct->AddRef();
     mStyleStructs[aSID] = aStyleStruct;
     return old && old->ReleaseWithoutDestroying() == 0;
   }
 
@@ -115,19 +112,16 @@ public:
     }
   }
   bool ClearStyleData(nsStyleStructID aSID) {
     bool shouldDelete = mStyleStructs[aSID] &&
                         mStyleStructs[aSID]->ReleaseWithoutDestroying() == 0;
     mStyleStructs[aSID] = nullptr;
     return shouldDelete;
   }
-  void SwapStyleData(nsStyleStructID aSID, nsResetStyleData& aOther) {
-    std::swap(mStyleStructs[aSID], aOther.mStyleStructs[aSID]);
-  }
   bool ReplaceStyleData(nsStyleStructID aSID, nsStyleStruct* aStyleStruct) {
     MOZ_ASSERT(aStyleStruct);
     nsStyleStruct* old = mStyleStructs[aSID];
     aStyleStruct->AddRef();
     mStyleStructs[aSID] = aStyleStruct;
     return old && old->ReleaseWithoutDestroying() == 0;
   }
 

--- a/layout/style/nsStyleContext.cpp
+++ b/layout/style/nsStyleContext.cpp
@@ -1391,69 +1391,16 @@ nsStyleContext::LookupStruct(const nsACS
 #undef STYLE_STRUCT
   else
     return false;
   return true;
 }
 #endif
 
 void
-nsStyleContext::SwapStyleData(nsStyleContext* aNewContext, uint32_t aStructs)
-{
-  static_assert(nsStyleStructID_Length <= 32, "aStructs is not big enough");
-
-  for (nsStyleStructID i = nsStyleStructID_Inherited_Start;
-       i < nsStyleStructID_Inherited_Start + nsStyleStructID_Inherited_Count;
-       i = nsStyleStructID(i + 1)) {
-    uint32_t bit = nsCachedStyleData::GetBitForSID(i);
-    if (!(aStructs & bit)) {
-      continue;
-    }
-    nsStyleStruct* thisData = mCachedInheritedData.GetStyleData(i);
-    nsStyleStruct* otherData = aNewContext->mCachedInheritedData.GetStyleData(i);
-    if (mBits & bit) {
-      if (thisData == otherData) {
-        DebugOnly<bool> shouldDelete = mCachedInheritedData.ClearStyleData(i);
-        MOZ_ASSERT(!shouldDelete, "style struct refcount shouldn't be 0 when it "
-                                  "is stored in two style contexts");
-      }
-    } else if (!(aNewContext->mBits & bit) && thisData && otherData) {
-      mCachedInheritedData.SwapStyleData(i, aNewContext->mCachedInheritedData);
-    }
-  }
-
-  for (nsStyleStructID i = nsStyleStructID_Reset_Start;
-       i < nsStyleStructID_Reset_Start + nsStyleStructID_Reset_Count;
-       i = nsStyleStructID(i + 1)) {
-    uint32_t bit = nsCachedStyleData::GetBitForSID(i);
-    if (!(aStructs & bit)) {
-      continue;
-    }
-    if (!mCachedResetData) {
-      mCachedResetData = new (mRuleNode->PresContext()) nsResetStyleData;
-    }
-    if (!aNewContext->mCachedResetData) {
-      aNewContext->mCachedResetData =
-        new (mRuleNode->PresContext()) nsResetStyleData;
-    }
-    nsStyleStruct* thisData = mCachedResetData->GetStyleData(i);
-    nsStyleStruct* otherData = aNewContext->mCachedResetData->GetStyleData(i);
-    if (mBits & bit) {
-      if (thisData == otherData) {
-        DebugOnly<bool> shouldDelete = mCachedResetData->ClearStyleData(i);
-        MOZ_ASSERT(!shouldDelete, "style struct refcount shouldn't be 0 when it "
-                                  "is stored in two style contexts");
-      }
-    } else if (!(aNewContext->mBits & bit) && thisData && otherData) {
-      mCachedResetData->SwapStyleData(i, *aNewContext->mCachedResetData);
-    }
-  }
-}
-
-void
 nsStyleContext::ClearCachedInheritedStyleDataOnDescendants(uint32_t aStructs)
 {
   if (mChild) {
     nsStyleContext* child = mChild;
     do {
       child->DoClearCachedInheritedStyleDataOnDescendants(aStructs);
       child = child->mNextSibling;
     } while (mChild != child);

--- a/layout/style/nsStyleContext.h
+++ b/layout/style/nsStyleContext.h
@@ -390,36 +390,16 @@ public:
    *
    * This function violates style context tree immutability, and
    * is a very low-level function and should only be used after verifying
    * many conditions that make it safe to call.
    */
   void MoveTo(nsStyleContext* aNewParent);
 
   /**
-   * Swaps owned style struct pointers between this and aNewContext, on
-   * the assumption that aNewContext is the new style context for a frame
-   * and this is the old one.  aStructs indicates which structs to consider
-   * swapping; only those which are owned in both this and aNewContext
-   * will be swapped.
-   *
-   * Additionally, if there are identical struct pointers for one of the
-   * structs indicated by aStructs, and it is not an owned struct on this,
-   * then the cached struct slot on this will be set to null.  If the struct
-   * has been swapped on an ancestor, this style context (being the old one)
-   * will be left caching the struct pointer on the new ancestor, despite
-   * inheriting from the old ancestor.  This is not normally a problem, as
-   * this style context will usually be destroyed by being released at the
-   * end of ElementRestyler::Restyle; but for style contexts held on to outside
-   * of the frame, we need to clear out the cached pointer so that if we need
-   * it again we'll re-fetch it from the new ancestor.
-   */
-  void SwapStyleData(nsStyleContext* aNewContext, uint32_t aStructs);
-
-  /**
    * On each descendant of this style context, clears out any cached inherited
    * structs indicated in aStructs.
    */
   void ClearCachedInheritedStyleDataOnDescendants(uint32_t aStructs);
 
   /**
    * Sets the NS_STYLE_INELIGIBLE_FOR_SHARING bit on this style context
    * and its descendants.  If it finds a descendant that has the bit