--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -10247,16 +10247,26 @@ IsFrameScrolledOutOfView(nsIFrame *aFram
 }
 
 bool
 nsIFrame::IsScrolledOutOfView()
 {
   return IsFrameScrolledOutOfView(this);
 }
 
+/* virtual */
+void
+nsIFrame::DoUpdateStyleOfOwnedAnonBoxes(ServoStyleSet& aStyleSet,
+                                      nsStyleChangeList& aChangeList,
+                                      nsChangeHint aHintForThisFrame)
+{
+  MOZ_ASSERT(!(GetStateBits() & NS_FRAME_OWNS_ANON_BOXES));
+  MOZ_ASSERT(false, "Why did this get called?");
+}
+
 nsIFrame::CaretPosition::CaretPosition()
   : mContentOffset(0)
 {
 }
 
 nsIFrame::CaretPosition::~CaretPosition()
 {
 }

--- a/layout/generic/nsFrameStateBits.h
+++ b/layout/generic/nsFrameStateBits.h
@@ -261,16 +261,20 @@ FRAME_STATE_BIT(Generic, 52, NS_FRAME_HA
 
 // Frame is not displayed directly due to it being, or being under, an SVG
 // <defs> element or an SVG resource element (<mask>, <pattern>, etc.)
 FRAME_STATE_BIT(Generic, 53, NS_FRAME_IS_NONDISPLAY)
 
 // Frame has a LayerActivityProperty property
 FRAME_STATE_BIT(Generic, 54, NS_FRAME_HAS_LAYER_ACTIVITY_PROPERTY)
 
+// Frame owns anonymous boxes whose style contexts it will need to update during
+// a stylo tree traversal.
+FRAME_STATE_BIT(Generic, 55, NS_FRAME_OWNS_ANON_BOXES)
+
 // Set for all descendants of MathML sub/supscript elements (other than the
 // base frame) to indicate that the SSTY font feature should be used.
 FRAME_STATE_BIT(Generic, 58, NS_FRAME_MATHML_SCRIPT_DESCENDANT)
 
 // This state bit is set on frames within token MathML elements if the
 // token represents an <mi> tag whose inner HTML consists of a single
 // non-whitespace character to allow special rendering behaviour.
 FRAME_STATE_BIT(Generic, 59, NS_FRAME_IS_IN_SINGLE_CHAR_MI)

--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -34,16 +34,17 @@
 #include "mozilla/ReflowOutput.h"
 #include "nsITheme.h"
 #include "nsLayoutUtils.h"
 #include "nsQueryFrame.h"
 #include "nsStringGlue.h"
 #include "nsStyleContext.h"
 #include "nsStyleStruct.h"
 #include "Visibility.h"
+#include "nsChangeHint.h"
 
 #ifdef ACCESSIBILITY
 #include "mozilla/a11y/AccTypes.h"
 #endif
 
 /**
  * New rules of reflow:
  * 1. you get a WillReflow() followed by a Reflow() followed by a DidReflow() in order
@@ -76,30 +77,32 @@ class nsDisplayListSet;
 class nsDisplayList;
 class gfxSkipChars;
 class gfxSkipCharsIterator;
 class gfxContext;
 class nsLineList_iterator;
 class nsAbsoluteContainingBlock;
 class nsIContent;
 class nsContainerFrame;
+class nsStyleChangeList;
 
 struct nsPeekOffsetStruct;
 struct nsPoint;
 struct nsRect;
 struct nsSize;
 struct nsMargin;
 struct CharacterDataChangeInfo;
 
 namespace mozilla {
 
 enum class CSSPseudoElementType : uint8_t;
 class EventStates;
 struct ReflowInput;
 class ReflowOutput;
+class ServoStyleSet;
 
 namespace layers {
 class Layer;
 } // namespace layers
 
 namespace gfx {
 class Matrix;
 } // namespace gfx
@@ -3041,16 +3044,45 @@ public:
    *     or nullptr if the style context is for display:contents content.
    * @return The style context that should be the parent of this frame's
    *         style context.  Null is permitted, and means that this frame's
    *         style context should be the root of the style context tree.
    */
   virtual nsStyleContext* GetParentStyleContext(nsIFrame** aProviderFrame) const = 0;
 
   /**
+   * Called by ServoRestyleManager to update the style contexts of anonymous
+   * boxes directly associtated with this frame.  The passed-in ServoStyleSet
+   * can be used to create new style contexts as needed.
+   *
+   * This function will be called after this frame's style context has already
+   * been updated.  This function will only be called on frames which have the
+   * NS_FRAME_OWNS_ANON_BOXES bit set.
+   *
+   * The nsStyleChangeList can be used to append additional changes.  It's
+   * guaranteed to already have a change in it for this frame and this frame's
+   * content and a change hint of aHintForThisFrame.
+   */
+  void UpdateStyleOfOwnedAnonBoxes(mozilla::ServoStyleSet& aStyleSet,
+                                   nsStyleChangeList& aChangeList,
+                                   nsChangeHint aHintForThisFrame) {
+    if (GetStateBits() & NS_FRAME_OWNS_ANON_BOXES) {
+      DoUpdateStyleOfOwnedAnonBoxes(aStyleSet, aChangeList, aHintForThisFrame);
+    }
+  }
+
+  /**
+   * Hook subclasses can override to actually implement updating of style of
+   * owned anon boxes.
+   */
+  virtual void DoUpdateStyleOfOwnedAnonBoxes(mozilla::ServoStyleSet& aStyleSet,
+                                             nsStyleChangeList& aChangeList,
+                                             nsChangeHint aHintForThisFrame);
+
+  /**
    * Determines whether a frame is visible for painting;
    * taking into account whether it is painting a selection or printing.
    */
   bool IsVisibleForPainting(nsDisplayListBuilder* aBuilder);
   /**
    * Determines whether a frame is visible for painting or collapsed;
    * taking into account whether it is painting a selection or printing,
    */