--- a/xpcom/ds/TimeStamp.h
+++ b/xpcom/ds/TimeStamp.h
@@ -206,18 +206,27 @@ public:
   /**
    * Return true if this is the "null" moment
    */
   bool IsNull() const { return mValue == 0; }
   /**
    * Return a timestamp reflecting the current elapsed system time. This
    * is monotonically increasing (i.e., does not decrease) over the
    * lifetime of this process' XPCOM session.
+   *
+   * Now() is trying to ensure the best possible precision on each platform,
+   * at least one millisecond.
+   *
+   * NowLoRes() has been introduced to workaround performance problems of
+   * QueryPerformanceCounter on the Windows platform.  NowLoRes() is giving
+   * lower precision, usually 15.6 ms, but with very good performance benefit.
+   * Use it for measurements of longer times, like >200ms timeouts.
    */
-  static TimeStamp Now();
+  static TimeStamp Now() { return Now(true); }
+  static TimeStamp NowLoRes() { return Now(false); }
   /**
    * Compute the difference between two timestamps. Both must be non-null.
    */
   TimeDuration operator-(const TimeStamp& aOther) const {
     MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
     MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
     PR_STATIC_ASSERT(-INT64_MAX > INT64_MIN);
     int64_t ticks = int64_t(mValue - aOther.mValue);
@@ -293,16 +302,18 @@ public:
   static NS_HIDDEN_(nsresult) Startup();
   static NS_HIDDEN_(void) Shutdown();
 
 private:
   friend struct IPC::ParamTraits<mozilla::TimeStamp>;
 
   TimeStamp(TimeStampValue aValue) : mValue(aValue) {}
 
+  static TimeStamp Now(bool aHighResolution);
+
   /**
    * When built with PRIntervalTime, a value of 0 means this instance
    * is "null". Otherwise, the low 32 bits represent a PRIntervalTime,
    * and the high 32 bits represent a counter of the number of
    * rollovers of PRIntervalTime that we've seen. This counter starts
    * at 1 to avoid a real time colliding with the "null" value.
    * 
    * PR_INTERVAL_MAX is set at 100,000 ticks per second. So the minimum

--- a/xpcom/ds/TimeStamp_darwin.cpp
+++ b/xpcom/ds/TimeStamp_darwin.cpp
@@ -151,14 +151,14 @@ TimeStamp::Startup()
 }
 
 void
 TimeStamp::Shutdown()
 {
 }
 
 TimeStamp
-TimeStamp::Now()
+TimeStamp::Now(bool aHighResolution)
 {
   return TimeStamp(ClockTime());
 }
 
 }

--- a/xpcom/ds/TimeStamp_posix.cpp
+++ b/xpcom/ds/TimeStamp_posix.cpp
@@ -163,14 +163,14 @@ TimeStamp::Startup()
 }
 
 void
 TimeStamp::Shutdown()
 {
 }
 
 TimeStamp
-TimeStamp::Now()
+TimeStamp::Now(bool aHighResolution)
 {
   return TimeStamp(ClockTimeNs());
 }
 
 }

--- a/xpcom/ds/TimeStamp_windows.cpp
+++ b/xpcom/ds/TimeStamp_windows.cpp
@@ -532,20 +532,20 @@ TimeStamp::Startup()
 
 void
 TimeStamp::Shutdown()
 {
   DeleteCriticalSection(&sTimeStampLock);
 }
 
 TimeStamp
-TimeStamp::Now()
+TimeStamp::Now(bool aHighResolution)
 {
   // sUseQPC is volatile
-  bool useQPC = sUseQPC;
+  bool useQPC = (aHighResolution && sUseQPC);
 
   // Both values are in [mt] units.
   ULONGLONG QPC = useQPC ? PerformanceCounter() : uint64_t(0);
   ULONGLONG GTC = ms2mt(sGetTickCount64());
   return TimeStamp(TimeStampValue(GTC, QPC, useQPC));
 }
 
 } // namespace mozilla