--- a/view/nsView.cpp
+++ b/view/nsView.cpp
@@ -1077,18 +1077,19 @@ nsView::DidCompositeWindow(uint64_t aTra
                            const TimeStamp& aCompositeEnd)
 {
   nsIPresShell* presShell = mViewManager->GetPresShell();
   if (presShell) {
     nsAutoScriptBlocker scriptBlocker;
 
     nsPresContext* context = presShell->GetPresContext();
     nsRootPresContext* rootContext = context->GetRootPresContext();
-    MOZ_ASSERT(rootContext, "rootContext must be valid.");
-    rootContext->NotifyDidPaintForSubtree(aTransactionId, aCompositeEnd);
+    if (rootContext) {
+      rootContext->NotifyDidPaintForSubtree(aTransactionId, aCompositeEnd);
+    }
 
     // If the two timestamps are identical, this was likely a fake composite
     // event which wouldn't be terribly useful to display.
     if (aCompositeStart == aCompositeEnd) {
       return;
     }
 
     nsIDocShell* docShell = context->GetDocShell();