--- a/toolkit/recordreplay/ProcessRecordReplay.cpp
+++ b/toolkit/recordreplay/ProcessRecordReplay.cpp
@@ -147,16 +147,19 @@ RecordReplayInterface_Initialize(int aAr
 
   InitializeTriggers();
   InitializeWeakPointers();
   InitializeMemorySnapshots();
   Thread::SpawnAllThreads();
   InitializeCountdownThread();
   SetupDirtyMemoryHandler();
 
+  // Don't create a stylo thread pool when recording or replaying.
+  putenv((char*) "STYLO_THREADS=1");
+
   thread->SetPassThrough(false);
 
   Lock::InitializeLocks();
   InitializeRewindState();
 
   gInitialized = true;
 }