--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -7975,16 +7975,20 @@ PresShell::DispatchEventToDOM(WidgetEven
     } else if (mDocument) {
       eventTarget = do_QueryInterface(mDocument);
       // If we don't have any content, the callback wouldn't probably
       // do nothing.
       eventCBPtr = nullptr;
     }
   }
   if (eventTarget) {
+    if (aEvent->IsBlockedForFingerprintingResistance()) {
+      aEvent->mFlags.mOnlySystemGroupDispatchInContent = true;
+    }
+
     if (aEvent->mClass == eCompositionEventClass) {
       IMEStateManager::DispatchCompositionEvent(eventTarget, mPresContext,
                                                 aEvent->AsCompositionEvent(),
                                                 aStatus, eventCBPtr);
     } else {
       EventDispatcher::Dispatch(eventTarget, mPresContext,
                                 aEvent, nullptr, aStatus, eventCBPtr);
     }

--- a/widget/BasicEvents.h
+++ b/widget/BasicEvents.h
@@ -857,16 +857,20 @@ public:
    * Whether the event should cause a DOM event.
    */
   bool IsAllowedToDispatchDOMEvent() const;
   /**
    * Whether the event should be dispatched in system group.
    */
   bool IsAllowedToDispatchInSystemGroup() const;
   /**
+   * Whether the event should be blocked for fingerprinting resistance.
+   */
+  bool IsBlockedForFingerprintingResistance() const;
+  /**
    * Initialize mComposed
    */
   void SetDefaultComposed()
   {
     switch (mClass) {
       case eCompositionEventClass:
         mFlags.mComposed = mMessage == eCompositionStart ||
                            mMessage == eCompositionUpdate ||

--- a/widget/WidgetEventImpl.cpp
+++ b/widget/WidgetEventImpl.cpp
@@ -505,16 +505,34 @@ bool
 WidgetEvent::IsAllowedToDispatchInSystemGroup() const
 {
   // We don't expect to implement default behaviors with pointer events because
   // if we do, prevent default on mouse events can't prevent default behaviors
   // anymore.
   return mClass != ePointerEventClass;
 }
 
+bool
+WidgetEvent::IsBlockedForFingerprintingResistance() const
+{
+  if (mClass == eKeyboardEventClass &&
+      nsContentUtils::ShouldResistFingerprinting()) {
+    const WidgetKeyboardEvent* keyboardEvent = AsKeyboardEvent();
+
+    if (keyboardEvent->mKeyNameIndex == KEY_NAME_INDEX_Alt     ||
+        keyboardEvent->mKeyNameIndex == KEY_NAME_INDEX_Shift   ||
+        keyboardEvent->mKeyNameIndex == KEY_NAME_INDEX_Control ||
+        keyboardEvent->mKeyNameIndex == KEY_NAME_INDEX_AltGraph) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 /******************************************************************************
  * mozilla::WidgetEvent
  *
  * Misc methods.
  ******************************************************************************/
 
 static dom::EventTarget*
 GetTargetForDOMEvent(nsIDOMEventTarget* aTarget)