--- a/layout/style/ServoBindings.cpp
+++ b/layout/style/ServoBindings.cpp
@@ -15,16 +15,17 @@
 #include "nsDOMTokenList.h"
 #include "nsIContentInlines.h"
 #include "nsIDOMNode.h"
 #include "nsIDocument.h"
 #include "nsIFrame.h"
 #include "nsINode.h"
 #include "nsIPrincipal.h"
 #include "nsNameSpaceManager.h"
+#include "nsRuleNode.h"
 #include "nsString.h"
 #include "nsStyleStruct.h"
 #include "nsStyleUtil.h"
 #include "nsTArray.h"
 
 #include "mozilla/EventStates.h"
 #include "mozilla/ServoElementSnapshot.h"
 #include "mozilla/ServoRestyleManager.h"
@@ -318,16 +319,22 @@ Gecko_GetServoDeclarationBlock(RawGeckoE
 {
   const nsAttrValue* attr = aElement->GetParsedAttr(nsGkAtoms::style);
   if (!attr || attr->Type() != nsAttrValue::eServoCSSDeclaration) {
     return nullptr;
   }
   return attr->GetServoCSSDeclarationValue();
 }
 
+void
+Gecko_FillAllBackgroundLists(nsStyleImageLayers* aLayers, uint32_t aMaxLen)
+{
+  nsRuleNode::FillAllBackgroundLists(*aLayers, aMaxLen);
+}
+
 template <typename Implementor>
 static nsIAtom*
 AtomAttrValue(Implementor* aElement, nsIAtom* aName)
 {
   const nsAttrValue* attr = aElement->GetParsedAttr(aName);
   return attr ? attr->GetAtomValue() : nullptr;
 }
 

--- a/layout/style/ServoBindings.h
+++ b/layout/style/ServoBindings.h
@@ -256,16 +256,17 @@ void Gecko_ResetStyleCoord(nsStyleUnit* 
 // Set an nsStyleCoord to a computed `calc()` value
 void Gecko_SetStyleCoordCalcValue(nsStyleUnit* unit, nsStyleUnion* value, nsStyleCoord::CalcValue calc);
 
 void Gecko_CopyClipPathValueFrom(mozilla::StyleClipPath* dst, const mozilla::StyleClipPath* src);
 
 void Gecko_DestroyClipPath(mozilla::StyleClipPath* clip);
 mozilla::StyleBasicShape* Gecko_NewBasicShape(mozilla::StyleBasicShapeType type);
 
+void Gecko_FillAllBackgroundLists(nsStyleImageLayers* layers, uint32_t max_len);
 NS_DECL_THREADSAFE_FFI_REFCOUNTING(nsStyleCoord::Calc, Calc);
 
 // Style-struct management.
 #define STYLE_STRUCT(name, checkdata_cb)                                       \
   struct nsStyle##name;                                                        \
   void Gecko_Construct_nsStyle##name(nsStyle##name* ptr);                      \
   void Gecko_CopyConstruct_nsStyle##name(nsStyle##name* ptr,                   \
                                          const nsStyle##name* other);          \

--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -7178,16 +7178,55 @@ FillBackgroundPositionCoordList(
   for (uint32_t sourceLayer = 0, destLayer = aItemCount;
        destLayer < aFillCount;
        ++sourceLayer, ++destLayer) {
     aLayers[destLayer].mPosition.*aResultLocation =
       aLayers[sourceLayer].mPosition.*aResultLocation;
   }
 }
 
+/* static */
+void
+nsRuleNode::FillAllBackgroundLists(nsStyleImageLayers& aImage,
+                                   uint32_t aMaxItemCount)
+{
+  // Delete any extra items.  We need to keep layers in which any
+  // property was specified.
+  aImage.mLayers.TruncateLengthNonZero(aMaxItemCount);
+
+  uint32_t fillCount = aImage.mImageCount;
+  FillBackgroundList(aImage.mLayers,
+                     &nsStyleImageLayers::Layer::mImage,
+                     aImage.mImageCount, fillCount);
+  FillBackgroundList(aImage.mLayers,
+                     &nsStyleImageLayers::Layer::mRepeat,
+                     aImage.mRepeatCount, fillCount);
+  FillBackgroundList(aImage.mLayers,
+                     &nsStyleImageLayers::Layer::mAttachment,
+                     aImage.mAttachmentCount, fillCount);
+  FillBackgroundList(aImage.mLayers,
+                     &nsStyleImageLayers::Layer::mClip,
+                     aImage.mClipCount, fillCount);
+  FillBackgroundList(aImage.mLayers,
+                     &nsStyleImageLayers::Layer::mBlendMode,
+                     aImage.mBlendModeCount, fillCount);
+  FillBackgroundList(aImage.mLayers,
+                     &nsStyleImageLayers::Layer::mOrigin,
+                     aImage.mOriginCount, fillCount);
+  FillBackgroundPositionCoordList(aImage.mLayers,
+                                  &Position::mXPosition,
+                                  aImage.mPositionXCount, fillCount);
+  FillBackgroundPositionCoordList(aImage.mLayers,
+                                  &Position::mYPosition,
+                                  aImage.mPositionYCount, fillCount);
+  FillBackgroundList(aImage.mLayers,
+                     &nsStyleImageLayers::Layer::mSize,
+                     aImage.mSizeCount, fillCount);
+}
+
 const void*
 nsRuleNode::ComputeBackgroundData(void* aStartStruct,
                                   const nsRuleData* aRuleData,
                                   nsStyleContext* aContext,
                                   nsRuleNode* aHighestNode,
                                   const RuleDetail aRuleDetail,
                                   const RuleNodeCacheConditions aConditions)
 {
@@ -7299,48 +7338,17 @@ nsRuleNode::ComputeBackgroundData(void* 
                         bg->mImage.mLayers,
                         parentBG->mImage.mLayers,
                         &nsStyleImageLayers::Layer::mSize,
                         initialSize, parentBG->mImage.mSizeCount,
                         bg->mImage.mSizeCount, maxItemCount, rebuild,
                         conditions);
 
   if (rebuild) {
-    // Delete any extra items.  We need to keep layers in which any
-    // property was specified.
-    bg->mImage.mLayers.TruncateLengthNonZero(maxItemCount);
-
-    uint32_t fillCount = bg->mImage.mImageCount;
-    FillBackgroundList(bg->mImage.mLayers,
-                       &nsStyleImageLayers::Layer::mImage,
-                       bg->mImage.mImageCount, fillCount);
-    FillBackgroundList(bg->mImage.mLayers,
-                       &nsStyleImageLayers::Layer::mRepeat,
-                       bg->mImage.mRepeatCount, fillCount);
-    FillBackgroundList(bg->mImage.mLayers,
-                       &nsStyleImageLayers::Layer::mAttachment,
-                       bg->mImage.mAttachmentCount, fillCount);
-    FillBackgroundList(bg->mImage.mLayers,
-                       &nsStyleImageLayers::Layer::mClip,
-                       bg->mImage.mClipCount, fillCount);
-    FillBackgroundList(bg->mImage.mLayers,
-                       &nsStyleImageLayers::Layer::mBlendMode,
-                       bg->mImage.mBlendModeCount, fillCount);
-    FillBackgroundList(bg->mImage.mLayers,
-                       &nsStyleImageLayers::Layer::mOrigin,
-                       bg->mImage.mOriginCount, fillCount);
-    FillBackgroundPositionCoordList(bg->mImage.mLayers,
-                                    &Position::mXPosition,
-                                    bg->mImage.mPositionXCount, fillCount);
-    FillBackgroundPositionCoordList(bg->mImage.mLayers,
-                                    &Position::mYPosition,
-                                    bg->mImage.mPositionYCount, fillCount);
-    FillBackgroundList(bg->mImage.mLayers,
-                       &nsStyleImageLayers::Layer::mSize,
-                       bg->mImage.mSizeCount, fillCount);
+    FillAllBackgroundLists(bg->mImage, maxItemCount);
   }
 
   // Now that the dust has settled, register the images with the document
   bg->mImage.TrackImages(aContext->PresContext());
 
   COMPUTE_END_RESET(Background, bg)
 }
 

--- a/layout/style/nsRuleNode.h
+++ b/layout/style/nsRuleNode.h
@@ -1048,16 +1048,21 @@ public:
                            nsStyleContext* aStyleContext,
                            nscolor& aResult);
 
   static bool ParentHasPseudoElementData(nsStyleContext* aContext);
 
   static void ComputeTimingFunction(const nsCSSValue& aValue,
                                     nsTimingFunction& aResult);
 
+  // Fill unspecified layers by cycling through their values
+  // till they all are of lenght aMaxItemCount
+  static void FillAllBackgroundLists(nsStyleImageLayers& aLayers,
+                                     uint32_t aMaxItemCount);
+
 private:
 #ifdef DEBUG
   // non-inline helper function to allow assertions without incomplete
   // type errors
   bool ContextHasCachedData(nsStyleContext* aContext, nsStyleStructID aSID);
 #endif
 
   // Store style struct on the style context and tell the style context