--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -1004,33 +1004,39 @@ nsDisplayListBuilder::EnterPresShell(nsI
   RefPtr<nsCaret> caret = state->mPresShell->GetCaret();
   state->mCaretFrame = caret->GetPaintGeometry(&state->mCaretRect);
   if (state->mCaretFrame) {
     mFramesMarkedForDisplay.AppendElement(state->mCaretFrame);
     MarkFrameForDisplay(state->mCaretFrame, nullptr);
   }
 
   nsPresContext* pc = aReferenceFrame->PresContext();
-  pc->GetDocShell()->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+  nsCOMPtr<nsIDocShell> docShell = pc->GetDocShell();
+  if (docShell) {
+    docShell->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+  }
   mIsInChromePresContext = pc->IsChrome();
 }
 
 void
 nsDisplayListBuilder::LeavePresShell(nsIFrame* aReferenceFrame)
 {
   NS_ASSERTION(CurrentPresShellState()->mPresShell ==
       aReferenceFrame->PresContext()->PresShell(),
       "Presshell mismatch");
 
   ResetMarkedFramesForDisplayList();
   mPresShellStates.SetLength(mPresShellStates.Length() - 1);
 
   if (!mPresShellStates.IsEmpty()) {
     nsPresContext* pc = CurrentPresContext();
-    pc->GetDocShell()->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+    nsCOMPtr<nsIDocShell> docShell = pc->GetDocShell();
+    if (docShell) {
+      docShell->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+    }
     mIsInChromePresContext = pc->IsChrome();
   }
 }
 
 void
 nsDisplayListBuilder::ResetMarkedFramesForDisplayList()
 {
   // Unmark and pop off the frames marked for display in this pres shell.