--- a/layout/base/nsFrameManager.h
+++ b/layout/base/nsFrameManager.h
@@ -58,101 +58,129 @@ struct UndisplayedNode : public LinkedLi
  *
  * Do not add virtual methods (a vtable pointer) or members to this class, or
  * else you'll break the validity of the reinterpret_cast in nsIPresShell's
  * FrameManager() method.
  */
 class nsFrameManager : public nsFrameManagerBase
 {
   typedef mozilla::layout::FrameChildListID ChildListID;
+  typedef mozilla::UndisplayedNode UndisplayedNode;
 
 public:
   explicit nsFrameManager(nsIPresShell* aPresShell) {
     mPresShell = aPresShell;
     MOZ_ASSERT(mPresShell, "need a pres shell");
   }
   ~nsFrameManager();
 
   /*
    * After Destroy is called, it is an error to call any FrameManager methods.
    * Destroy should be called when the frame tree managed by the frame
    * manager is no longer being displayed.
    */
   void Destroy();
 
-  // Mapping undisplayed content
+
+  // display:none and display:contents content does not get an nsIFrame.  To
+  // enable the style context for such content to be obtained we store the
+  // contexts in a couple of hash tables.  The following methods provide the
+  // API that's used to set, reset, obtain and clear these style contexts.
+
+  /**
+   * Register the style context for the display:none content, aContent.
+   */
+  void SetUndisplayedContent(nsIContent* aContent,
+                             nsStyleContext* aStyleContext);
+
+  /**
+   * Register the style context for the display:contents content, aContent.
+   */
+  void SetDisplayContents(nsIContent* aContent, nsStyleContext* aStyleContext);
+
+  /**
+   * Change the style context for the display:none content, aContent.
+   */
+  void ChangeUndisplayedContent(nsIContent* aContent,
+                                nsStyleContext* aStyleContext)
+  {
+    ChangeStyleContextInMap(mDisplayNoneMap, aContent, aStyleContext);
+  }
+
+  /**
+   * Change the style context for the display:contents content, aContent.
+   */
+  void ChangeDisplayContents(nsIContent* aContent,
+                             nsStyleContext* aStyleContext)
+  {
+    ChangeStyleContextInMap(mDisplayContentsMap, aContent, aStyleContext);
+  }
+
+  /**
+   * Get the style context for the display:none content, aContent.
+   */
   nsStyleContext* GetUndisplayedContent(const nsIContent* aContent)
   {
     if (!mDisplayNoneMap) {
       return nullptr;
     }
     return GetStyleContextInMap(mDisplayNoneMap, aContent);
   }
-  mozilla::UndisplayedNode*
-    GetAllUndisplayedContentIn(nsIContent* aParentContent);
-  void SetUndisplayedContent(nsIContent* aContent,
-                             nsStyleContext* aStyleContext);
-  void ChangeUndisplayedContent(nsIContent* aContent,
-                                nsStyleContext* aStyleContext)
-  {
-    ChangeStyleContextInMap(mDisplayNoneMap, aContent, aStyleContext);
-  }
 
-  void ClearUndisplayedContentIn(nsIContent* aContent,
-                                 nsIContent* aParentContent);
-
-  // display:contents related methods:
   /**
-   * Return the registered display:contents style context for aContent, if any.
+   * Get the style context for the display:contents content, aContent.
    */
   nsStyleContext* GetDisplayContentsStyleFor(const nsIContent* aContent)
   {
     if (!mDisplayContentsMap) {
       return nullptr;
     }
     return GetStyleContextInMap(mDisplayContentsMap, aContent);
   }
 
   /**
-   * Return the linked list of UndisplayedNodes containing the registered
-   * display:contents children of aParentContent, if any.
+   * Return a linked list of style contexts registered for display:none
+   * children of aParentContent.
    */
-  mozilla::UndisplayedNode* GetAllDisplayContentsIn(nsIContent* aParentContent);
+  UndisplayedNode* GetAllUndisplayedContentIn(nsIContent* aParentContent);
+
+  /**
+   * Return a linked list of style contexts registered for display:contents
+   * children of aParentContent.
+   */
+  UndisplayedNode* GetAllDisplayContentsIn(nsIContent* aParentContent);
 
   /**
    * Return the relevant undisplayed node for a given content with display:
    * contents style.
    */
-  mozilla::UndisplayedNode* GetDisplayContentsNodeFor(
-      const nsIContent* aContent) {
+  UndisplayedNode* GetDisplayContentsNodeFor(const nsIContent* aContent)
+  {
     if (!mDisplayContentsMap) {
       return nullptr;
     }
     return GetUndisplayedNodeInMapFor(mDisplayContentsMap, aContent);
   }
 
   /**
-   * Register aContent having a display:contents style context.
-   */
-  void SetDisplayContents(nsIContent* aContent, nsStyleContext* aStyleContext);
-  /**
-   * Change the registered style context for aContent to aStyleContext.
+   * Unregister the style context for the display:none content, aContent,
+   * if any.  If found, then also unregisters the style contexts for any
+   * display:contents and display:none descendants of aContent.
    */
-  void ChangeDisplayContents(nsIContent* aContent,
-                             nsStyleContext* aStyleContext)
-  {
-    ChangeStyleContextInMap(mDisplayContentsMap, aContent, aStyleContext);
-  }
+  void ClearUndisplayedContentIn(nsIContent* aContent,
+                                 nsIContent* aParentContent);
 
   /**
-   * Unregister the display:contents style context for aContent, if any.
-   * If found, then also unregister any display:contents and display:none
-   * style contexts for its descendants.
+   * Unregister the style context for the display:contents content, aContent,
+   * if any.  If found, then also unregisters the style contexts for any
+   * display:contents and display:none descendants of aContent.
    */
-  void ClearDisplayContentsIn(nsIContent* aContent, nsIContent* aParentContent);
+  void ClearDisplayContentsIn(nsIContent* aContent,
+                              nsIContent* aParentContent);
+
 
   // Functions for manipulating the frame model
   void AppendFrames(nsContainerFrame* aParentFrame,
                     ChildListID aListID,
                     nsFrameList& aFrameList);
 
   void InsertFrames(nsContainerFrame* aParentFrame,
                     ChildListID aListID,