--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -4766,16 +4766,18 @@ ScrollFrameHelper::CreateAnonymousConten
   if (canHaveHorizontal && canHaveVertical) {
     nodeInfo = nodeInfoManager->GetNodeInfo(nsGkAtoms::scrollcorner, nullptr,
                                             kNameSpaceID_XUL,
                                             nsINode::ELEMENT_NODE);
     NS_TrustedNewXULElement(getter_AddRefs(mScrollCornerContent), nodeInfo.forget());
     if (mIsRoot) {
       mScrollCornerContent->SetProperty(nsGkAtoms::docLevelNativeAnonymousContent,
                                         reinterpret_cast<void*>(true));
+      mScrollCornerContent->SetAttr(kNameSpaceID_None, nsGkAtoms::root_,
+                                    NS_LITERAL_STRING("true"), false);
     }
     if (!aElements.AppendElement(mScrollCornerContent))
       return NS_ERROR_OUT_OF_MEMORY;
   }
 
   return NS_OK;
 }