diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 8f0620a0fafe..cabd8b3771ef 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -368,12 +368,12 @@ IterPerformanceStats(JSContext* cx,
             continue;
         }
         js::AutoCompartment autoCompartment(cx, compartment);
-        PerformanceGroup* ownGroup = compartment->performanceMonitoring.getOwnGroup(cx);
+        mozilla::RefPtr<PerformanceGroup> ownGroup = compartment->performanceMonitoring.getOwnGroup();
         if (ownGroup->data.ticks == 0) {
             // Don't report compartments that have never been used.
             continue;
         }
-        PerformanceGroup* sharedGroup = compartment->performanceMonitoring.getSharedGroup(cx);
+        mozilla::RefPtr<PerformanceGroup> sharedGroup = compartment->performanceMonitoring.getSharedGroup(cx);
         if (!(*walker)(cx,
                        ownGroup->data, ownGroup->uid, &sharedGroup->uid,
                        closure)) {
@@ -383,7 +383,7 @@ IterPerformanceStats(JSContext* cx,
     }
 
     // Finally, report the process stats
-    *processStats = rt->stopwatch.performance;
+    *processStats = rt->stopwatch.performance.getOwnGroup()->data;
     return true;
 }
 
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 0027fee36da4..d0ddb5ad5865 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -13,6 +13,7 @@
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/Range.h"
 #include "mozilla/RangedPtr.h"
+#include "mozilla/RefPtr.h"
 
 #include <stdarg.h>
 #include <stddef.h>
@@ -5514,15 +5515,22 @@ struct PerformanceGroup {
         stopwatch_ = nullptr;
     }
 
-    explicit PerformanceGroup(JSContext* cx, void* key);
-    ~PerformanceGroup()
-    {
-        MOZ_ASSERT(refCount_ == 0);
-    }
-  private:
+    // Refcounting. For use with mozilla::RefPtr.
+    void AddRef();
+    void Release();
+
+    // Construct a PerformanceGroup for a single compartment.
+    explicit PerformanceGroup(JSRuntime* rt);
+
+    // Construct a PerformanceGroup for a group of compartments.
+    explicit PerformanceGroup(JSContext* rt, void* key);
+
+private:
     PerformanceGroup& operator=(const PerformanceGroup&) = delete;
     PerformanceGroup(const PerformanceGroup&) = delete;
 
+    JSRuntime* runtime_;
+
     // The stopwatch currently monitoring the group,
     // or `nullptr` if none. Used ony for comparison.
     const AutoStopwatch* stopwatch_;
@@ -5534,20 +5542,14 @@ struct PerformanceGroup {
     // The hash key for this PerformanceGroup.
     void* const key_;
 
-    // Increment/decrement the refcounter, return the updated value.
-    uint64_t incRefCount() {
-        MOZ_ASSERT(refCount_ + 1 > 0);
-        return ++refCount_;
-    }
-    uint64_t decRefCount() {
-        MOZ_ASSERT(refCount_ > 0);
-        return --refCount_;
-    }
-    friend struct PerformanceGroupHolder;
-
-private:
-    // A reference counter. Maintained by PerformanceGroupHolder.
+    // A reference counter.
     uint64_t refCount_;
+
+
+    // `true` if this PerformanceGroup may be shared by several
+    // compartments, `false` if it is dedicated to a single
+    // compartment.
+    const bool isSharedGroup_;
 };
 
 //
@@ -5564,7 +5566,7 @@ struct PerformanceGroupHolder {
     js::PerformanceGroup* getSharedGroup(JSContext*);
 
     // Get the own group.
-    js::PerformanceGroup* getOwnGroup(JSContext*);
+    js::PerformanceGroup* getOwnGroup();
 
     // `true` if the this holder is currently associated to a shared
     // PerformanceGroup, `false` otherwise. Use this method to avoid
@@ -5584,8 +5586,6 @@ struct PerformanceGroupHolder {
 
     explicit PerformanceGroupHolder(JSRuntime* runtime)
       : runtime_(runtime)
-      , sharedGroup_(nullptr)
-      , ownGroup_(nullptr)
     {   }
     ~PerformanceGroupHolder();
 
@@ -5600,8 +5600,8 @@ struct PerformanceGroupHolder {
     // The PerformanceGroups held by this object.
     // Initially set to `nullptr` until the first call to `getGroup`.
     // May be reset to `nullptr` by a call to `unlink`.
-    js::PerformanceGroup* sharedGroup_;
-    js::PerformanceGroup* ownGroup_;
+    mozilla::RefPtr<js::PerformanceGroup> sharedGroup_;
+    mozilla::RefPtr<js::PerformanceGroup> ownGroup_;
 };
 
 /**
diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index 37bbb7ff52b0..f686b70aaa56 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -389,22 +389,6 @@ class AutoStopwatch final
     // loop.  Used only for comparison.
     uint64_t iteration_;
 
-    // `true` if this object is currently used to monitor performance
-    // for a shared PerformanceGroup, `false` otherwise, i.e. if the
-    // stopwatch mechanism is off or if another stopwatch is already
-    // in charge of monitoring for the same PerformanceGroup.
-    bool isMonitoringForGroup_;
-
-    // `true` if this object is currently used to monitor performance
-    // for a single compartment, `false` otherwise, i.e. if the
-    // stopwatch mechanism is off or if another stopwatch is already
-    // in charge of monitoring for the same PerformanceGroup.
-    bool isMonitoringForSelf_;
-
-    // `true` if this stopwatch is the topmost stopwatch on the stack
-    // for this event, `false` otherwise.
-    bool isMonitoringForTop_;
-
     // `true` if we are monitoring jank, `false` otherwise.
     bool isMonitoringJank_;
     // `true` if we are monitoring CPOW, `false` otherwise.
@@ -415,6 +399,20 @@ class AutoStopwatch final
     uint64_t systemTimeStart_;
     uint64_t CPOWTimeStart_;
 
+   // The performance group shared by this compartment and possibly
+   // others, or `nullptr` if another AutoStopwatch is already in
+   // charge of monitoring that group.
+   mozilla::RefPtr<js::PerformanceGroup> sharedGroup_;
+
+   // The toplevel group, representing the entire process, or `nullptr`
+   // if another AutoStopwatch is already in charge of monitoring that group.
+   mozilla::RefPtr<js::PerformanceGroup> topGroup_;
+
+   // The performance group specific to this compartment, or
+   // `nullptr` if another AutoStopwatch is already in charge of
+   // monitoring that group.
+   mozilla::RefPtr<js::PerformanceGroup> ownGroup_;
+
    public:
     // If the stopwatch is active, constructing an instance of
     // AutoStopwatch causes it to become the current owner of the
@@ -424,9 +422,6 @@ class AutoStopwatch final
     explicit inline AutoStopwatch(JSContext* cx MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
       : cx_(cx)
       , iteration_(0)
-      , isMonitoringForGroup_(false)
-      , isMonitoringForSelf_(false)
-      , isMonitoringForTop_(false)
       , isMonitoringJank_(false)
       , isMonitoringCPOW_(false)
       , userTimeStart_(0)
@@ -442,52 +437,23 @@ class AutoStopwatch final
         JSRuntime* runtime = cx_->runtime();
         iteration_ = runtime->stopwatch.iteration;
 
-        PerformanceGroup* sharedGroup = compartment->performanceMonitoring.getSharedGroup(cx);
-        if (!sharedGroup) {
-            // Either this Runtime is not configured for Performance Monitoring, or we couldn't
-            // allocate the group, or there was a problem with the hashtable.
-            return;
-        }
+        sharedGroup_ = acquireGroup(compartment->performanceMonitoring.getSharedGroup(cx));
+        if (sharedGroup_)
+            topGroup_ = acquireGroup(runtime->stopwatch.performance.getOwnGroup());
 
-        if (!sharedGroup->hasStopwatch(iteration_)) {
-            // We are now in charge of monitoring this group for the tick,
-            // until destruction of `this` or until we enter a nested event
-            // loop and `iteration_` is incremented.
-            sharedGroup->acquireStopwatch(iteration_, this);
-            isMonitoringForGroup_ = true;
-        }
+        if (runtime->stopwatch.isMonitoringPerCompartment())
+            ownGroup_ = acquireGroup(compartment->performanceMonitoring.getOwnGroup());
 
-        PerformanceGroup* ownGroup = nullptr;
-        if (runtime->stopwatch.isMonitoringPerCompartment()) {
-            // As above, but for the group representing just this compartment.
-            ownGroup = compartment->performanceMonitoring.getOwnGroup(cx);
-            if (!ownGroup->hasStopwatch(iteration_)) {
-                ownGroup->acquireStopwatch(iteration_, this);
-                isMonitoringForSelf_ = true;
-            }
-        }
-
-        if (runtime->stopwatch.isEmpty) {
-            // This is the topmost stopwatch on the stack.
-            // It will be in charge of updating the per-process
-            // performance data.
-            runtime->stopwatch.isEmpty = false;
-            isMonitoringForTop_ = true;
-
-            MOZ_ASSERT(isMonitoringForGroup_);
-        }
-
-        if (!isMonitoringForGroup_ && !isMonitoringForSelf_) {
+        if (!sharedGroup_ && !ownGroup_) {
             // We are not in charge of monitoring anything.
-            // (isMonitoringForTop_ implies isMonitoringForGroup_,
-            // so we do not need to check it)
             return;
         }
 
         enter();
     }
-    ~AutoStopwatch() {
-        if (!isMonitoringForGroup_ && !isMonitoringForSelf_) {
+    ~AutoStopwatch()
+    {
+        if (!sharedGroup_ && !ownGroup_) {
             // We are not in charge of monitoring anything.
             // (isMonitoringForTop_ implies isMonitoringForGroup_,
             // so we do not need to check it)
@@ -505,31 +471,19 @@ class AutoStopwatch final
             return;
         }
 
+        releaseGroup(sharedGroup_);
+        releaseGroup(topGroup_);
+        releaseGroup(ownGroup_);
+
         // Finish and commit measures
         exit();
-
-        // Now release groups.
-        if (isMonitoringForGroup_) {
-            PerformanceGroup* sharedGroup = compartment->performanceMonitoring.getSharedGroup(cx_);
-            MOZ_ASSERT(sharedGroup);
-            sharedGroup->releaseStopwatch(iteration_, this);
-        }
-
-        if (isMonitoringForSelf_) {
-            PerformanceGroup* ownGroup = compartment->performanceMonitoring.getOwnGroup(cx_);
-            MOZ_ASSERT(ownGroup);
-            ownGroup->releaseStopwatch(iteration_, this);
-        }
-
-        if (isMonitoringForTop_)
-            runtime->stopwatch.isEmpty = true;
     }
    private:
     void enter() {
         JSRuntime* runtime = cx_->runtime();
 
         if (runtime->stopwatch.isMonitoringCPOW()) {
-            CPOWTimeStart_ = runtime->stopwatch.performance.totalCPOWTime;
+            CPOWTimeStart_ = runtime->stopwatch.performance.getOwnGroup()->data.totalCPOWTime;
             isMonitoringCPOW_ = true;
         }
 
@@ -563,46 +517,54 @@ class AutoStopwatch final
         uint64_t CPOWTimeDelta = 0;
         if (isMonitoringCPOW_ && runtime->stopwatch.isMonitoringCPOW()) {
             // We were monitoring CPOW when we entered and we still are.
-            CPOWTimeDelta = runtime->stopwatch.performance.totalCPOWTime - CPOWTimeStart_;
+            CPOWTimeDelta = runtime->stopwatch.performance.getOwnGroup()->data.totalCPOWTime - CPOWTimeStart_;
 
         }
         commitDeltasToGroups(userTimeDelta, systemTimeDelta, CPOWTimeDelta);
     }
 
-    void commitDeltasToGroups(uint64_t userTimeDelta,
-                              uint64_t systemTimeDelta,
-                              uint64_t CPOWTimeDelta)
-    {
-        JSCompartment* compartment = cx_->compartment();
+    // Attempt to acquire a group
+    // If the group is `null` or if the group already has a stopwatch,
+    // do nothing and return `null`.
+    // Otherwise, bind the group to `this` for the current iteration
+    // and return `group`.
+    PerformanceGroup* acquireGroup(PerformanceGroup* group) {
+        if (!group)
+            return nullptr;
 
-        PerformanceGroup* sharedGroup = compartment->performanceMonitoring.getSharedGroup(cx_);
-        MOZ_ASSERT(sharedGroup);
-        applyDeltas(userTimeDelta, systemTimeDelta, CPOWTimeDelta, sharedGroup->data);
+        if (group->hasStopwatch(iteration_))
+            return nullptr;
 
-        if (isMonitoringForSelf_) {
-            PerformanceGroup* ownGroup = compartment->performanceMonitoring.getOwnGroup(cx_);
-            MOZ_ASSERT(ownGroup);
-            applyDeltas(userTimeDelta, systemTimeDelta, CPOWTimeDelta, ownGroup->data);
-        }
-
-        if (isMonitoringForTop_) {
-            JSRuntime* runtime = cx_->runtime();
-            applyDeltas(userTimeDelta, systemTimeDelta, CPOWTimeDelta, runtime->stopwatch.performance);
-        }
+        group->acquireStopwatch(iteration_, this);
+        return group;
     }
 
+    // Release a group.
+    // Noop if `group` is null or if `this` is not the stopwatch
+    // of `group` for the current iteration.
+    void releaseGroup(PerformanceGroup* group) {
+        if (group)
+            group->releaseStopwatch(iteration_, this);
+    }
 
-    void applyDeltas(uint64_t userTimeDelta,
-                     uint64_t systemTimeDelta,
-                     uint64_t CPOWTimeDelta,
-                     PerformanceData& data) const {
+    void commitDeltasToGroups(uint64_t userTimeDelta, uint64_t systemTimeDelta,
+                              uint64_t CPOWTimeDelta) const {
+        applyDeltas(userTimeDelta, systemTimeDelta, CPOWTimeDelta, sharedGroup_);
+        applyDeltas(userTimeDelta, systemTimeDelta, CPOWTimeDelta, topGroup_);
+        applyDeltas(userTimeDelta, systemTimeDelta, CPOWTimeDelta, ownGroup_);
+    }
 
-        data.ticks++;
+    void applyDeltas(uint64_t userTimeDelta, uint64_t systemTimeDelta,
+                     uint64_t CPOWTimeDelta, PerformanceGroup* group) const {
+        if (!group)
+            return;
+
+        group->data.ticks++;
 
         uint64_t totalTimeDelta = userTimeDelta + systemTimeDelta;
-        data.totalUserTime += userTimeDelta;
-        data.totalSystemTime += systemTimeDelta;
-        data.totalCPOWTime += CPOWTimeDelta;
+        group->data.totalUserTime += userTimeDelta;
+        group->data.totalSystemTime += systemTimeDelta;
+        group->data.totalCPOWTime += CPOWTimeDelta;
 
         // Update an array containing the number of times we have missed
         // at least 2^0 successive ms, 2^1 successive ms, ...
@@ -612,10 +574,10 @@ class AutoStopwatch final
         size_t i = 0;
         uint64_t duration = 1000;
         for (i = 0, duration = 1000;
-             i < ArrayLength(data.durations) && duration < totalTimeDelta;
+             i < ArrayLength(group->data.durations) && duration < totalTimeDelta;
              ++i, duration *= 2)
         {
-            data.durations[i]++;
+            group->data.durations[i]++;
         }
     }
 
diff --git a/js/src/vm/Runtime.cpp b/js/src/vm/Runtime.cpp
index 145c1f5a9e5f..c579600c8401 100644
--- a/js/src/vm/Runtime.cpp
+++ b/js/src/vm/Runtime.cpp
@@ -222,7 +222,8 @@ JSRuntime::JSRuntime(JSRuntime* parentRuntime)
     largeAllocationFailureCallback(nullptr),
     oomCallback(nullptr),
     debuggerMallocSizeOf(ReturnZeroSize),
-    lastAnimationTime(0)
+    lastAnimationTime(0),
+    stopwatch(thisFromCtor())
 {
     setGCStoreBufferPtr(&gc.storeBuffer);
 
@@ -930,40 +931,17 @@ js::PerformanceGroupHolder::getHashKey(JSContext* cx)
 void
 js::PerformanceGroupHolder::unlink()
 {
-    if (ownGroup_) {
-        js_delete(ownGroup_);
-        ownGroup_ = nullptr;
-    }
-
-    if (!sharedGroup_) {
-        // The group has never been instantiated.
-        return;
-    }
-
-    js::PerformanceGroup* group = sharedGroup_;
+    ownGroup_ = nullptr;
     sharedGroup_ = nullptr;
-
-    if (group->decRefCount() > 0) {
-        // The group has at least another owner.
-        return;
-    }
-
-
-    JSRuntime::Stopwatch::Groups::Ptr ptr =
-        runtime_->stopwatch.groups().lookup(group->key_);
-    MOZ_ASSERT(ptr);
-    runtime_->stopwatch.groups().remove(ptr);
-    js_delete(group);
 }
 
 PerformanceGroup*
-js::PerformanceGroupHolder::getOwnGroup(JSContext* cx)
+js::PerformanceGroupHolder::getOwnGroup()
 {
     if (ownGroup_)
         return ownGroup_;
 
-    ownGroup_ = runtime_->new_<PerformanceGroup>(cx, nullptr);
-    return ownGroup_;
+    return ownGroup_ = runtime_->new_<PerformanceGroup>(runtime_);
 }
 
 PerformanceGroup*
@@ -985,31 +963,58 @@ js::PerformanceGroupHolder::getSharedGroup(JSContext* cx)
         if (!sharedGroup_)
             return nullptr;
 
-        if (!runtime_->stopwatch.groups().add(ptr, key, sharedGroup_)) {
-            js_delete(sharedGroup_);
-            sharedGroup_ = nullptr;
-            return nullptr;
-        }
+        runtime_->stopwatch.groups().add(ptr, key, sharedGroup_);
     }
 
-    sharedGroup_->incRefCount();
-
     return sharedGroup_;
 }
 
 PerformanceData*
 js::GetPerformanceData(JSRuntime* rt)
 {
-    return &rt->stopwatch.performance;
+    return &rt->stopwatch.performance.getOwnGroup()->data;
 }
 
-js::PerformanceGroup::PerformanceGroup(JSContext* cx, void* key)
-  : uid(cx->runtime()->stopwatch.uniqueId())
-  , stopwatch_(nullptr)
-  , iteration_(0)
-  , key_(key)
-  , refCount_(0)
+js::PerformanceGroup::PerformanceGroup(JSRuntime* rt)
+  : uid(rt->stopwatch.uniqueId()),
+    runtime_(rt),
+    stopwatch_(nullptr),
+    iteration_(0),
+    key_(nullptr),
+    refCount_(0),
+    isSharedGroup_(false)
+{ }
+
+ js::PerformanceGroup::PerformanceGroup(JSContext* cx, void* key)
+   : uid(cx->runtime()->stopwatch.uniqueId()),
+     runtime_(cx->runtime()),
+     stopwatch_(nullptr),
+     iteration_(0),
+     key_(key),
+     refCount_(0),
+     isSharedGroup_(true)
+{ }
+
+void
+js::PerformanceGroup::AddRef()
 {
+    ++refCount_;
+}
+
+void
+js::PerformanceGroup::Release()
+{
+    MOZ_ASSERT(refCount_ > 0);
+    --refCount_;
+    if (refCount_ > 0)
+        return;
+    if (!isSharedGroup_)
+        return;
+
+    JSRuntime::Stopwatch::Groups::Ptr ptr = runtime_->stopwatch.groups().lookup(key_);
+    MOZ_ASSERT(ptr);
+    runtime_->stopwatch.groups().remove(ptr);
+    js_delete(this);
 }
 
 void
diff --git a/js/src/vm/Runtime.h b/js/src/vm/Runtime.h
index 11982419c8b7..4b2f1e0c2981 100644
--- a/js/src/vm/Runtime.h
+++ b/js/src/vm/Runtime.h
@@ -1512,6 +1512,11 @@ struct JSRuntime : public JS::shadow::Runtime,
             return groups_;
         }
 
+        /**
+         * Performance data on the entire runtime.
+         */
+        js::PerformanceGroupHolder performance;
+
         /**
          * The number of times we have entered the event loop.
          * Used to reset counters whenever we enter the loop,
@@ -1523,17 +1528,6 @@ struct JSRuntime : public JS::shadow::Runtime,
          */
         uint64_t iteration;
 
-        /**
-         * `true` if no stopwatch has been registered for the
-         * current run of the event loop, `false` until then.
-         */
-        bool isEmpty;
-
-        /**
-         * Performance data on the entire runtime.
-         */
-        js::PerformanceData performance;
-
         /**
          * Callback used to ask the embedding to determine in which
          * Performance Group the current execution belongs. Typically, this is
@@ -1546,9 +1540,9 @@ struct JSRuntime : public JS::shadow::Runtime,
          */
         JSCurrentPerfGroupCallback currentPerfGroupCallback;
 
-        Stopwatch()
-          : iteration(0)
-          , isEmpty(true)
+        Stopwatch(JSRuntime* runtime)
+          : performance(runtime)
+          , iteration(0)
           , currentPerfGroupCallback(nullptr)
           , isMonitoringJank_(false)
           , isMonitoringCPOW_(false)
@@ -1565,7 +1559,6 @@ struct JSRuntime : public JS::shadow::Runtime,
          */
         void reset() {
             ++iteration;
-            isEmpty = true;
         }
         /**
          * Activate/deactivate stopwatch measurement of jank.