--- a/xpcom/base/CycleCollectedJSRuntime.h
+++ b/xpcom/base/CycleCollectedJSRuntime.h
@@ -97,28 +97,30 @@ struct CycleCollectorResults
     // not using uninitialized memory.
     Init();
   }
 
   void Init()
   {
     mForcedGC = false;
     mMergedZones = false;
+    mAnyManual = false;
     mVisitedRefCounted = 0;
     mVisitedGCed = 0;
     mFreedRefCounted = 0;
     mFreedGCed = 0;
     mFreedJSZones = 0;
     mNumSlices = 1;
     // mNumSlices is initialized to one, because we call Init() after the
     // per-slice increment of mNumSlices has already occurred.
   }
 
   bool mForcedGC;
   bool mMergedZones;
+  bool mAnyManual; // true if any slice of the CC was manually triggered, or at shutdown.
   uint32_t mVisitedRefCounted;
   uint32_t mVisitedGCed;
   uint32_t mFreedRefCounted;
   uint32_t mFreedGCed;
   uint32_t mFreedJSZones;
   uint32_t mNumSlices;
 };
 

--- a/xpcom/base/nsCycleCollector.cpp
+++ b/xpcom/base/nsCycleCollector.cpp
@@ -3589,16 +3589,20 @@ nsCycleCollector::Collect(ccType aCCType
   // If the CC started idle, it will call BeginCollection, which
   // will do FreeSnowWhite, so it doesn't need to be done here.
   if (!startedIdle) {
     TimeLog timeLog;
     FreeSnowWhite(true);
     timeLog.Checkpoint("Collect::FreeSnowWhite");
   }
 
+  if (aCCType != SliceCC) {
+    mResults.mAnyManual = true;
+  }
+
   ++mResults.mNumSlices;
 
   bool continueSlice = aBudget.isUnlimited() || !aPreferShorterSlices;
   do {
     switch (mIncrementalPhase) {
       case IdlePhase:
         PrintPhase("BeginCollection");
         BeginCollection(aCCType, aManualListener);
@@ -3774,16 +3778,17 @@ nsCycleCollector::BeginCollection(ccType
 
   if (mListener && NS_FAILED(mListener->Begin())) {
     mListener = nullptr;
   }
 
   // Set up the data structures for building the graph.
   mGraph.Init();
   mResults.Init();
+  mResults.mAnyManual = (aCCType != SliceCC);
   bool mergeZones = ShouldMergeZones(aCCType);
   mResults.mMergedZones = mergeZones;
 
   MOZ_ASSERT(!mBuilder, "Forgot to clear mBuilder");
   mBuilder = new CCGraphBuilder(mGraph, mResults, mJSRuntime, mListener,
                                 mergeZones);
 
   if (mJSRuntime) {