diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
index f33ded1c5f..5edf7dc4a5 100644
--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -4339,6 +4339,11 @@ WorkerPrivate::Constructor(JSContext* aCx,
     return nullptr;
   }
 
+  // From this point on (worker thread has been started) we
+  // must keep ourself alive. We can now only be cleared by
+  // ClearSelfAndParentEventTargetRef().
+  worker->mSelfRef = worker;
+
   worker->EnableDebugger();
 
   RefPtr<CompileScriptRunnable> compiler =
@@ -4348,8 +4353,6 @@ WorkerPrivate::Constructor(JSContext* aCx,
     return nullptr;
   }
 
-  worker->mSelfRef = worker;
-
   return worker.forget();
 }
 
diff --git a/mfbt/LinkedList.h b/mfbt/LinkedList.h
index a099d7597a..9d04e64c77 100644
--- a/mfbt/LinkedList.h
+++ b/mfbt/LinkedList.h
@@ -327,7 +327,8 @@ private:
   void setNextUnsafe(RawType aElem)
   {
     LinkedListElement *listElem = static_cast<LinkedListElement*>(aElem);
-    MOZ_ASSERT(!listElem->isInList());
+    if (listElem->isInList())
+      return;
 
     listElem->mNext = this->mNext;
     listElem->mPrev = this;
@@ -344,7 +345,8 @@ private:
   void setPreviousUnsafe(RawType aElem)
   {
     LinkedListElement<T>* listElem = static_cast<LinkedListElement<T>*>(aElem);
-    MOZ_ASSERT(!listElem->isInList());
+    if (listElem->isInList())
+      return;
 
     listElem->mNext = this;
     listElem->mPrev = this->mPrev;