diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index 482b98da2a45..b4029e4e2ca5 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -2101,9 +2101,12 @@ static nsIContent* GetNativeAnonymousSubtreeRoot(nsIContent* aContent)
     return nullptr;
   }
   auto* current = aContent;
+  // FIXME(emilio): This should not need to worry about current being null, but
+  // editor removes nodes in native anonymous subtrees, and we don't clean nodes
+  // from the current event content stack from ContentRemoved, so it can
+  // actually happen, see bug 1510208.
   while (current && !current->IsRootOfNativeAnonymousSubtree()) {
     current = current->GetFlattenedTreeParent();
-    MOZ_DIAGNOSTIC_ASSERT(current, "How?");
   }
   return current;
 }