--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -375,21 +375,16 @@ nsDOMWindowUtils::SetDisplayPortForEleme
     return NS_ERROR_DOM_SECURITY_ERR;
   }
 
   nsIPresShell* presShell = GetPresShell();
   if (!presShell) {
     return NS_ERROR_FAILURE;
   }
 
-  nsRect displayport(nsPresContext::CSSPixelsToAppUnits(aXPx),
-                     nsPresContext::CSSPixelsToAppUnits(aYPx),
-                     nsPresContext::CSSPixelsToAppUnits(aWidthPx),
-                     nsPresContext::CSSPixelsToAppUnits(aHeightPx));
-
   if (!aElement) {
     return NS_ERROR_INVALID_ARG;
   }
 
   nsCOMPtr<nsIContent> content = do_QueryInterface(aElement);
 
   if (!content) {
     return NS_ERROR_INVALID_ARG;
@@ -400,35 +395,38 @@ nsDOMWindowUtils::SetDisplayPortForEleme
   }
 
   DisplayPortPropertyData* currentData =
     static_cast<DisplayPortPropertyData*>(content->GetProperty(nsGkAtoms::DisplayPort));
   if (currentData && currentData->mPriority > aPriority) {
     return NS_OK;
   }
 
+  nsRect displayport(nsPresContext::CSSPixelsToAppUnits(aXPx),
+                     nsPresContext::CSSPixelsToAppUnits(aYPx),
+                     nsPresContext::CSSPixelsToAppUnits(aWidthPx),
+                     nsPresContext::CSSPixelsToAppUnits(aHeightPx));
+
   content->SetProperty(nsGkAtoms::DisplayPort,
                        new DisplayPortPropertyData(displayport, aPriority),
                        nsINode::DeleteProperty<DisplayPortPropertyData>);
 
   nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame();
-  if (rootScrollFrame) {
-    if (content == rootScrollFrame->GetContent()) {
-      // We are setting a root displayport for a document.
-      // The pres shell needs a special flag set.
-      presShell->SetIgnoreViewportScrolling(true);
-
-      // When the "font.size.inflation.minTwips" preference is set, the
-      // layout depends on the size of the screen.  Since when the size
-      // of the screen changes, the root displayport also changes, we
-      // hook in the needed updates here rather than adding a
-      // separate notification just for this change.
-      nsPresContext* presContext = GetPresContext();
-      MaybeReflowForInflationScreenWidthChange(presContext);
-    }
+  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);
+
+    // When the "font.size.inflation.minTwips" preference is set, the
+    // layout depends on the size of the screen.  Since when the size
+    // of the screen changes, the root displayport also changes, we
+    // hook in the needed updates here rather than adding a
+    // separate notification just for this change.
+    nsPresContext* presContext = GetPresContext();
+    MaybeReflowForInflationScreenWidthChange(presContext);
   }
 
   nsIFrame* rootFrame = presShell->FrameManager()->GetRootFrame();
   if (rootFrame) {
     rootFrame->SchedulePaint();
 
     // If we are hiding something that is a display root then send empty paint
     // transaction in order to release retained layers because it won't get
@@ -465,23 +463,16 @@ nsDOMWindowUtils::SetDisplayPortMarginsF
     return NS_ERROR_DOM_SECURITY_ERR;
   }
 
   nsIPresShell* presShell = GetPresShell();
   if (!presShell) {
     return NS_ERROR_FAILURE;
   }
 
-  // Note order change of arguments between our function signature and
-  // LayerMargin constructor.
-  LayerMargin displayportMargins(aTopMargin,
-                                 aRightMargin,
-                                 aBottomMargin,
-                                 aLeftMargin);
-
   if (!aElement) {
     return NS_ERROR_INVALID_ARG;
   }
 
   nsCOMPtr<nsIContent> content = do_QueryInterface(aElement);
 
   if (!content) {
     return NS_ERROR_INVALID_ARG;
@@ -492,27 +483,32 @@ nsDOMWindowUtils::SetDisplayPortMarginsF
   }
 
   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, aAlignment, aPriority),
                        nsINode::DeleteProperty<DisplayPortMarginsPropertyData>);
 
   nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame();
-  if (rootScrollFrame) {
-    if (content == rootScrollFrame->GetContent()) {
-      // We are setting a root displayport for a document.
-      // The pres shell needs a special flag set.
-      presShell->SetIgnoreViewportScrolling(true);
-    }
+  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();
   }
 
   return NS_OK;