--- a/dom/html/HTMLInputElement.cpp
+++ b/dom/html/HTMLInputElement.cpp
@@ -4124,17 +4124,18 @@ HTMLInputElement::SetValueOfRangeForUser
 
 void
 HTMLInputElement::StartNumberControlSpinnerSpin()
 {
   MOZ_ASSERT(!mNumberControlSpinnerIsSpinning);
 
   mNumberControlSpinnerIsSpinning = true;
 
-  nsRepeatService::GetInstance()->Start(HandleNumberControlSpin, this);
+  nsRepeatService::GetInstance()->Start(HandleNumberControlSpin, this,
+                                        NS_LITERAL_CSTRING("HandleNumberControlSpin"));
 
   // Capture the mouse so that we can tell if the pointer moves from one
   // spin button to the other, or to some other element:
   nsIPresShell::SetCapturingContent(this, CAPTURE_IGNOREALLOWED);
 
   nsNumberControlFrame* numberControlFrame =
     do_QueryFrame(GetPrimaryFrame());
   if (numberControlFrame) {

--- a/layout/xul/nsRepeatService.cpp
+++ b/layout/xul/nsRepeatService.cpp
@@ -38,23 +38,27 @@ nsRepeatService::GetInstance()
 }
 
 /*static*/ void
 nsRepeatService::Shutdown()
 {
   gRepeatService = nullptr;
 }
 
-void nsRepeatService::Start(Callback aCallback, void* aCallbackData,
-                            uint32_t aInitialDelay)
+void
+nsRepeatService::Start(Callback aCallback, void* aCallbackData,
+                       const nsACString& aCallbackName,
+                       uint32_t aInitialDelay)
 {
   NS_PRECONDITION(aCallback != nullptr, "null ptr");
 
   mCallback = aCallback;
   mCallbackData = aCallbackData;
+  mCallbackName = aCallbackName;
+
   nsresult rv;
   mRepeatTimer = do_CreateInstance("@mozilla.org/timer;1", &rv);
 
   if (NS_SUCCEEDED(rv))  {
     InitTimerCallback(aInitialDelay);
   }
 }
 
@@ -74,25 +78,25 @@ void nsRepeatService::Stop(Callback aCal
 
 void
 nsRepeatService::InitTimerCallback(uint32_t aInitialDelay)
 {
   if (!mRepeatTimer) {
     return;
   }
 
-  mRepeatTimer->InitWithFuncCallback([](nsITimer* aTimer, void* aClosure) {
+  mRepeatTimer->InitWithNamedFuncCallback([](nsITimer* aTimer, void* aClosure) {
     // Use gRepeatService instead of nsRepeatService::GetInstance() (because
     // we don't want nsRepeatService::GetInstance() to re-create a new instance
     // for us, if we happen to get invoked after nsRepeatService::Shutdown() has
     // nulled out gRepeatService).
     nsRepeatService* rs = gRepeatService;
     if (!rs) {
       return;
     }
 
     if (rs->mCallback) {
       rs->mCallback(rs->mCallbackData);
     }
 
     rs->InitTimerCallback(REPEAT_DELAY);
-  }, nullptr, aInitialDelay, nsITimer::TYPE_ONE_SHOT);
+  }, nullptr, aInitialDelay, nsITimer::TYPE_ONE_SHOT, mCallbackName.Data());
 }

--- a/layout/xul/nsRepeatService.h
+++ b/layout/xul/nsRepeatService.h
@@ -27,17 +27,21 @@ class nsRepeatService final
 public:
   typedef void (* Callback)(void* aData);
 
   ~nsRepeatService();
 
   // Start dispatching timer events to the callback. There is no memory
   // management of aData here; it is the caller's responsibility to call
   // Stop() before aData's memory is released.
-  void Start(Callback aCallback, void* aData,
+  //
+  // aCallbackName is the label of the callback, used to pass to
+  // InitWithNamedCallbackFunc.
+  void Start(Callback aCallback, void* aCallbackData,
+             const nsACString& aCallbackName,
              uint32_t aInitialDelay = INITAL_REPEAT_DELAY);
   // Stop dispatching timer events to the callback. If the repeat service
   // is not currently configured with the given callback and data, this
   // is just ignored.
   void Stop(Callback aCallback, void* aData);
 
   static nsRepeatService* GetInstance();
   static void Shutdown();
@@ -46,13 +50,14 @@ protected:
   nsRepeatService();
 
 private:
   // helper function to initialize callback function to mRepeatTimer
   void InitTimerCallback(uint32_t aInitialDelay);
 
   Callback           mCallback;
   void*              mCallbackData;
+  nsCString          mCallbackName;
   nsCOMPtr<nsITimer> mRepeatTimer;
 
 }; // class nsRepeatService
 
 #endif

--- a/layout/xul/nsScrollBoxFrame.cpp
+++ b/layout/xul/nsScrollBoxFrame.cpp
@@ -42,19 +42,22 @@ public:
 
 protected:
   explicit nsAutoRepeatBoxFrame(nsStyleContext* aContext):
     nsButtonBoxFrame(aContext) {}
   
   void StartRepeat() {
     if (IsActivatedOnHover()) {
       // No initial delay on hover.
-      nsRepeatService::GetInstance()->Start(Notify, this, 0);
+      nsRepeatService::GetInstance()->Start(Notify, this,
+                                            NS_LITERAL_CSTRING("DoMouseClick"),
+                                            0);
     } else {
-      nsRepeatService::GetInstance()->Start(Notify, this);
+      nsRepeatService::GetInstance()->Start(Notify, this,
+                                            NS_LITERAL_CSTRING("DoMouseClick"));
     }
   }
   void StopRepeat() {
     nsRepeatService::GetInstance()->Stop(Notify, this);
   }
   void Notify();
   static void Notify(void* aData) {
     static_cast<nsAutoRepeatBoxFrame*>(aData)->Notify();

--- a/layout/xul/nsScrollbarButtonFrame.h
+++ b/layout/xul/nsScrollbarButtonFrame.h
@@ -60,17 +60,18 @@ public:
   NS_IMETHOD HandleRelease(nsPresContext* aPresContext,
                            mozilla::WidgetGUIEvent* aEvent,
                            nsEventStatus* aEventStatus) override;
 
 protected:
   virtual void MouseClicked(mozilla::WidgetGUIEvent* aEvent) override;
 
   void StartRepeat() {
-    nsRepeatService::GetInstance()->Start(Notify, this);
+    nsRepeatService::GetInstance()->Start(Notify, this,
+                                          NS_LITERAL_CSTRING("nsScrollbarButtonFrame"));
   }
   void StopRepeat() {
     nsRepeatService::GetInstance()->Stop(Notify, this);
   }
   void Notify();
   static void Notify(void* aData) {
     static_cast<nsScrollbarButtonFrame*>(aData)->Notify();
   }

--- a/layout/xul/nsSliderFrame.h
+++ b/layout/xul/nsSliderFrame.h
@@ -162,17 +162,18 @@ private:
   void AddListener();
   void RemoveListener();
   bool isDraggingThumb();
 
   void SuppressDisplayport();
   void UnsuppressDisplayport();
 
   void StartRepeat() {
-    nsRepeatService::GetInstance()->Start(Notify, this);
+    nsRepeatService::GetInstance()->Start(Notify, this,
+                                          NS_LITERAL_CSTRING("nsSliderFrame"));
   }
   void StopRepeat() {
     nsRepeatService::GetInstance()->Stop(Notify, this);
   }
   void Notify();
   static void Notify(void* aData) {
     (static_cast<nsSliderFrame*>(aData))->Notify();
   }