diff --git a/xpcom/ds/nsExpirationTracker.h b/xpcom/ds/nsExpirationTracker.h
index 672256d1dc..53b4ceafdc 100644
--- a/xpcom/ds/nsExpirationTracker.h
+++ b/xpcom/ds/nsExpirationTracker.h
@@ -127,9 +127,15 @@ public:
    */
   nsresult AddObjectLocked(T* aObj, const AutoLock& aAutoLock)
   {
+    if (NS_WARN_IF(!aObj)) {
+      // Invalid object to add
+      return NS_ERROR_UNEXPECTED;
+    }
     nsExpirationState* state = aObj->GetExpirationState();
-    NS_ASSERTION(!state->IsTracked(),
-                 "Tried to add an object that's already tracked");
+    if (NS_WARN_IF(state->IsTracked())) {
+      // Tried to add an object that's already tracked.
+      return NS_ERROR_UNEXPECTED;
+    }
     nsTArray<T*>& generation = mGenerations[mNewestGeneration];
     uint32_t index = generation.Length();
     if (index > nsExpirationState::MAX_INDEX_IN_GENERATION) {
@@ -156,8 +162,15 @@ public:
    */
   void RemoveObjectLocked(T* aObj, const AutoLock& aAutoLock)
   {
+    if (NS_WARN_IF(!aObj)) {
+      // Invalid object to remove
+      return;
+    }
     nsExpirationState* state = aObj->GetExpirationState();
-    NS_ASSERTION(state->IsTracked(), "Tried to remove an object that's not tracked");
+    if (NS_WARN_IF(!state->IsTracked())) {
+      // Tried to remove an object that's not tracked
+      return;
+    }
     nsTArray<T*>& generation = mGenerations[state->mGeneration];
     uint32_t index = state->mIndexInGeneration;
     NS_ASSERTION(generation.Length() > index &&
@@ -458,11 +471,13 @@ class nsExpirationTracker : protected ::detail::SingleThreadedExpirationTracker<
   Lock mLock;
 
   AutoLock FakeLock() {
+    MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
     return AutoLock(mLock);
   }
 
   Lock& GetMutex() override
   {
+    MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
     return mLock;
   }