--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -429,44 +429,25 @@ nsDOMWindowUtils::SetDisplayPortMarginsF
   if (!content) {
     return NS_ERROR_INVALID_ARG;
   }
 
   if (content->GetCurrentDoc() != presShell->GetDocument()) {
     return NS_ERROR_INVALID_ARG;
   }
 
-  DisplayPortMarginsPropertyData* currentData =
-    static_cast<DisplayPortMarginsPropertyData*>(content->GetProperty(nsGkAtoms::DisplayPortMargins));
-  if (currentData && currentData->mPriority > aPriority) {
-    return NS_OK;
-  }
-
   // Note order change of arguments between our function signature and
   // LayerMargin constructor.
   LayerMargin displayportMargins(aTopMargin,
                                  aRightMargin,
                                  aBottomMargin,
                                  aLeftMargin);
 
-  content->SetProperty(nsGkAtoms::DisplayPortMargins,
-                       new DisplayPortMarginsPropertyData(displayportMargins, aAlignmentX, aAlignmentY, aPriority),
-                       nsINode::DeleteProperty<DisplayPortMarginsPropertyData>);
-
-  nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame();
-  if (rootScrollFrame && content == rootScrollFrame->GetContent()) {
-    // We are setting a root displayport for a document.
-    // The pres shell needs a special flag set.
-    presShell->SetIgnoreViewportScrolling(true);
-  }
-
-  nsIFrame* rootFrame = presShell->FrameManager()->GetRootFrame();
-  if (rootFrame) {
-    rootFrame->SchedulePaint();
-  }
+  nsLayoutUtils::SetDisplayPortMargins(content, presShell, displayportMargins,
+                                       aAlignmentX, aAlignmentY, aPriority);
 
   return NS_OK;
 }
 
 
 NS_IMETHODIMP
 nsDOMWindowUtils::SetDisplayPortBaseForElement(int32_t aX,
                                                int32_t aY,
@@ -492,18 +473,17 @@ nsDOMWindowUtils::SetDisplayPortBaseForE
   if (!content) {
     return NS_ERROR_INVALID_ARG;
   }
 
   if (content->GetCurrentDoc() != presShell->GetDocument()) {
     return NS_ERROR_INVALID_ARG;
   }
 
-  content->SetProperty(nsGkAtoms::DisplayPortBase, new nsRect(aX, aY, aWidth, aHeight),
-                       nsINode::DeleteProperty<nsRect>);
+  nsLayoutUtils::SetDisplayPortBase(content, nsRect(aX, aY, aWidth, aHeight));
 
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsDOMWindowUtils::SetCriticalDisplayPortForElement(float aXPx, float aYPx,
                                                    float aWidthPx, float aHeightPx,
                                                    nsIDOMElement* aElement)

--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -768,16 +768,51 @@ nsLayoutUtils::GetDisplayPort(nsIContent
       }
     }
   }
 
   return true;
 }
 
 void
+nsLayoutUtils::SetDisplayPortMargins(nsIContent* aContent,
+                                     nsIPresShell* aPresShell,
+                                     const LayerMargin& aMargins,
+                                     uint32_t aAlignmentX,
+                                     uint32_t aAlignmentY,
+                                     uint32_t aPriority,
+                                     RepaintMode aRepaintMode)
+{
+  DisplayPortMarginsPropertyData* currentData =
+    static_cast<DisplayPortMarginsPropertyData*>(aContent->GetProperty(nsGkAtoms::DisplayPortMargins));
+  if (currentData && currentData->mPriority > aPriority) {
+    return;
+  }
+
+  aContent->SetProperty(nsGkAtoms::DisplayPortMargins,
+                        new DisplayPortMarginsPropertyData(
+                            aMargins, aAlignmentX, aAlignmentY, aPriority),
+                        nsINode::DeleteProperty<DisplayPortMarginsPropertyData>);
+
+  nsIFrame* rootScrollFrame = aPresShell->GetRootScrollFrame();
+  if (rootScrollFrame && aContent == rootScrollFrame->GetContent()) {
+    // We are setting a root displayport for a document.
+    // The pres shell needs a special flag set.
+    aPresShell->SetIgnoreViewportScrolling(true);
+  }
+
+  if (aRepaintMode == RepaintMode::Repaint) {
+    nsIFrame* rootFrame = aPresShell->FrameManager()->GetRootFrame();
+    if (rootFrame) {
+      rootFrame->SchedulePaint();
+    }
+  }
+}
+
+void
 nsLayoutUtils::SetDisplayPortBase(nsIContent* aContent, const nsRect& aBase)
 {
   aContent->SetProperty(nsGkAtoms::DisplayPortBase, new nsRect(aBase),
                         nsINode::DeleteProperty<nsRect>);
 }
 
 bool
 nsLayoutUtils::GetCriticalDisplayPort(nsIContent* aContent, nsRect* aResult)

--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -122,16 +122,17 @@ class nsLayoutUtils
   typedef mozilla::gfx::DrawTarget DrawTarget;
   typedef mozilla::gfx::Rect Rect;
 
 public:
   typedef mozilla::layers::FrameMetrics FrameMetrics;
   typedef FrameMetrics::ViewID ViewID;
   typedef mozilla::CSSPoint CSSPoint;
   typedef mozilla::CSSSize CSSSize;
+  typedef mozilla::LayerMargin LayerMargin;
 
   /**
    * Finds previously assigned ViewID for the given content element, if any.
    * Returns whether a ViewID was previously assigned.
    */
   static bool FindIDFor(const nsIContent* aContent, ViewID* aOutViewId);
 
   /**
@@ -150,21 +151,48 @@ public:
    */
   static nsIScrollableFrame* FindScrollableFrameFor(ViewID aId);
 
   /**
    * Get display port for the given element.
    */
   static bool GetDisplayPort(nsIContent* aContent, nsRect *aResult = nullptr);
 
- /**
-  * Set the display port base rect for given element to be used with display
-  * port margins.
-  */
- static void SetDisplayPortBase(nsIContent* aContent, const nsRect& aBase);
+  MOZ_BEGIN_ENUM_CLASS(RepaintMode, uint8_t)
+    Repaint,
+    DoNotRepaint
+  MOZ_END_ENUM_CLASS(RepaintMode)
+
+  /**
+   * Set the display port margins for a content element to be used with a
+   * display port base (see SetDisplayPortBase()).
+   * See also nsIDOMWindowUtils.setDisplayPortMargins.
+   * @param aContent the content element for which to set the margins
+   * @param aPresShell the pres shell for the document containing the element
+   * @param aMargins the margins to set
+   * @param aAlignmentX, alignmentY the amount of pixels to which to align the
+   *                                displayport built by combining the base
+   *                                rect with the margins, in either direction
+   * @param aPriority a priority value to determine which margins take effect
+   *                  when multiple callers specify margins
+   * @param aRepaintMode whether to schedule a paint after setting the margins
+   */
+  static void SetDisplayPortMargins(nsIContent* aContent,
+                                    nsIPresShell* aPresShell,
+                                    const LayerMargin& aMargins,
+                                    uint32_t aAlignmentX,
+                                    uint32_t aAlignmentY,
+                                    uint32_t aPriority = 0,
+                                    RepaintMode aRepaintMode = RepaintMode::Repaint);
+
+  /**
+   * Set the display port base rect for given element to be used with display
+   * port margins.
+   */
+  static void SetDisplayPortBase(nsIContent* aContent, const nsRect& aBase);
 
   /**
    * Get the critical display port for the given element.
    */
   static bool GetCriticalDisplayPort(nsIContent* aContent, nsRect* aResult = nullptr);
 
   /**
    * Use heuristics to figure out the child list that