--- a/xpcom/base/CycleCollectedJSRuntime.cpp
+++ b/xpcom/base/CycleCollectedJSRuntime.cpp
@@ -872,25 +872,17 @@ nsCycleCollectionParticipant*
 CycleCollectedJSRuntime::ZoneParticipant()
 {
     return &mJSZoneCycleCollectorGlobal;
 }
 
 nsresult
 CycleCollectedJSRuntime::TraverseRoots(nsCycleCollectionNoteRootCallback &aCb)
 {
-  static bool gcHasRun = false;
-  if (!gcHasRun) {
-    uint32_t gcNumber = JS_GetGCParameter(mJSRuntime, JSGC_NUMBER);
-    if (!gcNumber) {
-      // Cannot cycle collect if GC has not run first!
-      MOZ_CRASH();
-    }
-    gcHasRun = true;
-  }
+  MOZ_ASSERT(!NeedCollect(), "Cannot cycle collect if GC has not run first!");
 
   TraverseNativeRoots(aCb);
 
   NoteWeakMapsTracer trc(mJSRuntime, TraceWeakMapping, aCb);
   js::TraceWeakMaps(&trc);
 
   return NS_OK;
 }