diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 90284e2e8f4f..bed180fb3060 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -8196,7 +8196,7 @@ nsresult nsContentUtils::SendMouseEvent(
     int32_t aButton, int32_t aButtons, int32_t aClickCount, int32_t aModifiers,
     bool aIgnoreRootScrollFrame, float aPressure,
     unsigned short aInputSourceArg, uint32_t aIdentifier, bool aToWindow,
-    bool* aPreventDefault, bool aIsDOMEventSynthesized,
+    PreventDefaultResult* aPreventDefault, bool aIsDOMEventSynthesized,
     bool aIsWidgetEventSynthesized) {
   nsPoint offset;
   nsCOMPtr<nsIWidget> widget = GetWidget(aPresShell, &offset);
@@ -8278,7 +8278,15 @@ nsresult nsContentUtils::SendMouseEvent(
     NS_ENSURE_SUCCESS(rv, rv);
   }
   if (aPreventDefault) {
-    *aPreventDefault = (status == nsEventStatus_eConsumeNoDefault);
+    if (status == nsEventStatus_eConsumeNoDefault) {
+      if (event.mFlags.mDefaultPreventedByContent) {
+        *aPreventDefault = PreventDefaultResult::ByContent;
+      } else {
+        *aPreventDefault = PreventDefaultResult::ByChrome;
+      }
+    } else {
+      *aPreventDefault = PreventDefaultResult::No;
+    }
   }
 
   return NS_OK;
@@ -10602,3 +10610,21 @@ nsCString nsContentUtils::TruncatedURLForDisplay(nsIURI* aURL,
   }
   return spec;
 }
+
+namespace mozilla {
+std::ostream& operator<<(std::ostream& aOut,
+                         const PreventDefaultResult aPreventDefaultResult) {
+  switch (aPreventDefaultResult) {
+    case PreventDefaultResult::No:
+      aOut << "unhandled";
+      break;
+    case PreventDefaultResult::ByContent:
+      aOut << "handled-by-content";
+      break;
+    case PreventDefaultResult::ByChrome:
+      aOut << "handled-by-chrome";
+      break;
+  }
+  return aOut;
+}
+}  // namespace mozilla
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index e97347037c37..edbd0eedbebf 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -245,6 +245,10 @@ struct EventNameMapping {
   bool mMaybeSpecialSVGorSMILEvent;
 };
 
+namespace mozilla {
+enum class PreventDefaultResult : uint8_t { No, ByContent, ByChrome };
+}
+
 class nsContentUtils {
   friend class nsAutoScriptBlockerSuppressNodeRemoved;
   typedef mozilla::dom::Element Element;
@@ -2916,8 +2920,8 @@ class nsContentUtils {
       float aY, int32_t aButton, int32_t aButtons, int32_t aClickCount,
       int32_t aModifiers, bool aIgnoreRootScrollFrame, float aPressure,
       unsigned short aInputSourceArg, uint32_t aIdentifier, bool aToWindow,
-      bool* aPreventDefault, bool aIsDOMEventSynthesized,
-      bool aIsWidgetEventSynthesized);
+      mozilla::PreventDefaultResult* aPreventDefault,
+      bool aIsDOMEventSynthesized, bool aIsWidgetEventSynthesized);
 
   static void FirePageShowEventForFrameLoaderSwap(
       nsIDocShellTreeItem* aItem,
@@ -3492,6 +3496,12 @@ nsContentUtils::InternalContentPolicyTypeToExternal(nsContentPolicyType aType) {
   }
 }
 
+namespace mozilla {
+std::ostream& operator<<(
+    std::ostream& aOut,
+    const mozilla::PreventDefaultResult aPreventDefaultResult);
+}  // namespace mozilla
+
 class MOZ_RAII nsAutoScriptBlocker {
  public:
   explicit nsAutoScriptBlocker() { nsContentUtils::AddScriptBlocker(); }
diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index ef7a48f631bc..b6cc4461ff96 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -725,10 +725,17 @@ nsDOMWindowUtils::SendMouseEventCommon(
     bool aToWindow, bool* aPreventDefault, bool aIsDOMEventSynthesized,
     bool aIsWidgetEventSynthesized, int32_t aButtons) {
   RefPtr<PresShell> presShell = GetPresShell();
-  return nsContentUtils::SendMouseEvent(
+  PreventDefaultResult preventDefaultResult;
+  nsresult rv = nsContentUtils::SendMouseEvent(
       presShell, aType, aX, aY, aButton, aButtons, aClickCount, aModifiers,
       aIgnoreRootScrollFrame, aPressure, aInputSourceArg, aPointerId, aToWindow,
-      aPreventDefault, aIsDOMEventSynthesized, aIsWidgetEventSynthesized);
+      &preventDefaultResult, aIsDOMEventSynthesized, aIsWidgetEventSynthesized);
+
+  if (aPreventDefault) {
+    *aPreventDefault = preventDefaultResult != PreventDefaultResult::No;
+  }
+
+  return rv;
 }
 
 NS_IMETHODIMP
diff --git a/gfx/layers/apz/util/APZCCallbackHelper.cpp b/gfx/layers/apz/util/APZCCallbackHelper.cpp
index f42825f09ed7..838c82257969 100644
--- a/gfx/layers/apz/util/APZCCallbackHelper.cpp
+++ b/gfx/layers/apz/util/APZCCallbackHelper.cpp
@@ -551,13 +551,14 @@ bool APZCCallbackHelper::DispatchMouseEvent(
     unsigned short aInputSourceArg, uint32_t aPointerId) {
   NS_ENSURE_TRUE(aPresShell, true);
 
-  bool defaultPrevented = false;
+  PreventDefaultResult preventDefaultResult;
   nsContentUtils::SendMouseEvent(
       aPresShell, aType, aPoint.x, aPoint.y, aButton,
       nsIDOMWindowUtils::MOUSE_BUTTONS_NOT_SPECIFIED, aClickCount, aModifiers,
       /* aIgnoreRootScrollFrame = */ false, 0, aInputSourceArg, aPointerId,
-      false, &defaultPrevented, false, /* aIsWidgetEventSynthesized = */ false);
-  return defaultPrevented;
+      false, &preventDefaultResult, false,
+      /* aIsWidgetEventSynthesized = */ false);
+  return preventDefaultResult != PreventDefaultResult::No;
 }
 
 void APZCCallbackHelper::FireSingleTapEvent(const LayoutDevicePoint& aPoint,