--- a/dom/performance/Performance.cpp
+++ b/dom/performance/Performance.cpp
@@ -101,17 +101,21 @@ Performance::Now()
   const double maxResolutionMs = 0.020;
   DOMHighResTimeStamp minimallyClamped = floor(rawTime / maxResolutionMs) * maxResolutionMs;
   return nsRFPService::ReduceTimePrecisionAsMSecs(minimallyClamped, GetRandomTimelineSeed());
 }
 
 DOMHighResTimeStamp
 Performance::NowUnclamped() const
 {
+#ifdef MOZ_FUZZYFOX
+  TimeDuration duration = TimeStamp::NowReally() - CreationTimeStamp();
+#else
   TimeDuration duration = TimeStamp::Now() - CreationTimeStamp();
+#endif
   return duration.ToMilliseconds();
 }
 
 DOMHighResTimeStamp
 Performance::TimeOrigin()
 {
   if (!mPerformanceService) {
     mPerformanceService = PerformanceService::GetOrCreate();