diff --git a/dom/base/nsJSEnvironment.cpp b/dom/base/nsJSEnvironment.cpp
index 7be9ff35605..3b4c4aa7279 100644
--- a/dom/base/nsJSEnvironment.cpp
+++ b/dom/base/nsJSEnvironment.cpp
@@ -2078,7 +2078,8 @@ nsJSContext::EndCycleCollectionCallback(CycleCollectorResults &aResults)
   Telemetry::Accumulate(Telemetry::CYCLE_COLLECTOR_MAX_PAUSE, gCCStats.mMaxSliceTime);
 
   if (!sLastCCEndTime.IsNull()) {
-    uint32_t timeBetween = TimeBetween(sLastCCEndTime, gCCStats.mBeginTime);
+    // TimeBetween returns milliseconds, but we want to report seconds.
+    uint32_t timeBetween = TimeBetween(sLastCCEndTime, gCCStats.mBeginTime) / 1000;
     Telemetry::Accumulate(Telemetry::CYCLE_COLLECTOR_TIME_BETWEEN, timeBetween);
   }
   sLastCCEndTime = endCCTimeStamp;