diff --git a/docshell/base/WindowContext.cpp b/docshell/base/WindowContext.cpp
index 958654207df4..bdc1fe7ac788 100644
--- a/docshell/base/WindowContext.cpp
+++ b/docshell/base/WindowContext.cpp
@@ -364,11 +364,11 @@ void WindowContext::DidSet(FieldIndex<IDX_SHEntryHasUserInteraction>,
   }
 }
 
-void WindowContext::DidSet(FieldIndex<IDX_UserActivationState>) {
+void WindowContext::DidSet(FieldIndex<IDX_UserActivationStateAndModifiers>) {
   MOZ_ASSERT_IF(!IsInProcess(), mUserGestureStart.IsNull());
-  USER_ACTIVATION_LOG("Set user gesture activation %" PRIu8
+  USER_ACTIVATION_LOG("Set user gesture activation 0x%02" PRIu8
                       " for %s browsing context 0x%08" PRIx64,
-                      static_cast<uint8_t>(GetUserActivationState()),
+                      GetUserActivationStateAndModifiers(),
                       XRE_IsParentProcess() ? "Parent" : "Child", Id());
   if (IsInProcess()) {
     USER_ACTIVATION_LOG(
@@ -484,11 +484,15 @@ void WindowContext::AddSecurityState(uint32_t aStateFlags) {
 }
 
 void WindowContext::NotifyUserGestureActivation() {
-  Unused << SetUserActivationState(UserActivation::State::FullActivated);
+  UserActivation::StateAndModifiers stateAndModifiers;
+  stateAndModifiers.SetState(UserActivation::State::FullActivated);
+  Unused << SetUserActivationStateAndModifiers(stateAndModifiers.GetRawData());
 }
 
 void WindowContext::NotifyResetUserGestureActivation() {
-  Unused << SetUserActivationState(UserActivation::State::None);
+  UserActivation::StateAndModifiers stateAndModifiers;
+  stateAndModifiers.SetState(UserActivation::State::None);
+  Unused << SetUserActivationStateAndModifiers(stateAndModifiers.GetRawData());
 }
 
 bool WindowContext::HasBeenUserGestureActivated() {
@@ -534,8 +538,11 @@ bool WindowContext::ConsumeTransientUserGestureActivation() {
     WindowContext* windowContext = aBrowsingContext->GetCurrentWindowContext();
     if (windowContext && windowContext->GetUserActivationState() ==
                              UserActivation::State::FullActivated) {
-      Unused << windowContext->SetUserActivationState(
-          UserActivation::State::HasBeenActivated);
+      auto stateAndModifiers = UserActivation::StateAndModifiers(
+          GetUserActivationStateAndModifiers());
+      stateAndModifiers.SetState(UserActivation::State::HasBeenActivated);
+      Unused << windowContext->SetUserActivationStateAndModifiers(
+          stateAndModifiers.GetRawData());
     }
   });
 
diff --git a/docshell/base/WindowContext.h b/docshell/base/WindowContext.h
index 890c658f912b..e5272ee486de 100644
--- a/docshell/base/WindowContext.h
+++ b/docshell/base/WindowContext.h
@@ -69,7 +69,8 @@ class BrowsingContextGroup;
   FIELD(HasBeforeUnload, bool)                                           \
   /* Controls whether the WindowContext is currently considered to be    \
    * activated by a gesture */                                           \
-  FIELD(UserActivationState, UserActivation::State)                      \
+  FIELD(UserActivationStateAndModifiers,                                 \
+        UserActivation::StateAndModifiers::DataT)                        \
   FIELD(EmbedderPolicy, nsILoadInfo::CrossOriginEmbedderPolicy)          \
   /* True if this document tree contained at least a HTMLMediaElement.   \
    * This should only be set on top level context. */                    \
@@ -194,6 +195,12 @@ class WindowContext : public nsISupports, public nsWrapperCache {
   // 'MIXED' state flags, and should only be called on the top window context.
   void AddSecurityState(uint32_t aStateFlags);
 
+  UserActivation::State GetUserActivationState() const {
+    return UserActivation::StateAndModifiers(
+               GetUserActivationStateAndModifiers())
+        .GetState();
+  }
+
   // This function would be called when its corresponding window is activated
   // by user gesture.
   void NotifyUserGestureActivation();
@@ -310,8 +317,9 @@ class WindowContext : public nsISupports, public nsWrapperCache {
   bool CanSet(FieldIndex<IDX_DelegatedExactHostMatchPermissions>,
               const PermissionDelegateHandler::DelegatedPermissionList& aValue,
               ContentParent* aSource);
-  bool CanSet(FieldIndex<IDX_UserActivationState>,
-              const UserActivation::State& aUserActivationState,
+  bool CanSet(FieldIndex<IDX_UserActivationStateAndModifiers>,
+              const UserActivation::StateAndModifiers::DataT&
+                  aUserActivationStateAndModifiers,
               ContentParent* aSource) {
     return true;
   }
@@ -344,7 +352,7 @@ class WindowContext : public nsISupports, public nsWrapperCache {
   void DidSet(FieldIndex<I>) {}
   template <size_t I, typename T>
   void DidSet(FieldIndex<I>, T&& aOldValue) {}
-  void DidSet(FieldIndex<IDX_UserActivationState>);
+  void DidSet(FieldIndex<IDX_UserActivationStateAndModifiers>);
 
   // Recomputes whether we can execute scripts in this WindowContext based on
   // the value of AllowJavascript() and whether scripts are allowed in the
diff --git a/dom/base/UserActivation.h b/dom/base/UserActivation.h
index c067bbc8c3f0..6accfa71291d 100644
--- a/dom/base/UserActivation.h
+++ b/dom/base/UserActivation.h
@@ -7,6 +7,7 @@
 #ifndef mozilla_dom_UserActivation_h
 #define mozilla_dom_UserActivation_h
 
+#include "mozilla/Assertions.h"
 #include "mozilla/EventForwards.h"
 #include "mozilla/TimeStamp.h"
 #include "nsCycleCollectionParticipant.h"
@@ -44,6 +45,73 @@ class UserActivation final : public nsISupports, public nsWrapperCache {
     EndGuard_
   };
 
+  class StateAndModifiers;
+
+  // Modifier keys held while the user activation.
+  class Modifiers {
+   public:
+    static constexpr uint8_t Shift = 0x10;
+    static constexpr uint8_t Meta = 0x20;
+    static constexpr uint8_t Control = 0x40;
+    static constexpr uint8_t Alt = 0x80;
+
+    static constexpr uint8_t Mask = 0xF0;
+
+    constexpr Modifiers() = default;
+    explicit constexpr Modifiers(uint8_t aModifiers) : mModifiers(aModifiers) {}
+
+    static constexpr Modifiers None() { return Modifiers(0); }
+
+    uint8_t GetRawData() const { return mModifiers; }
+
+    void SetShift() { mModifiers |= Shift; }
+    void SetMeta() { mModifiers |= Meta; }
+    void SetControl() { mModifiers |= Control; }
+    void SetAlt() { mModifiers |= Alt; }
+
+    bool IsShift() const { return mModifiers & Shift; }
+    bool IsMeta() const { return mModifiers & Meta; }
+    bool IsControl() const { return mModifiers & Control; }
+    bool IsAlt() const { return mModifiers & Alt; }
+
+   private:
+    uint8_t mModifiers = 0;
+
+    friend class StateAndModifiers;
+  };
+
+  // State and Modifiers encoded into single data, for WindowContext field.
+  class StateAndModifiers {
+   public:
+    using DataT = uint8_t;
+
+    constexpr StateAndModifiers() = default;
+    explicit constexpr StateAndModifiers(DataT aStateAndModifiers)
+        : mStateAndModifiers(aStateAndModifiers) {}
+
+    DataT GetRawData() const { return mStateAndModifiers; }
+
+    State GetState() const { return State(RawState()); }
+    void SetState(State aState) {
+      MOZ_ASSERT((uint8_t(aState) & Modifiers::Mask) == 0);
+      mStateAndModifiers = uint8_t(aState) | RawModifiers();
+    }
+
+    Modifiers GetModifiers() const { return Modifiers(RawModifiers()); }
+    void SetModifiers(Modifiers aModifiers) {
+      mStateAndModifiers = RawState() | aModifiers.mModifiers;
+    }
+
+   private:
+    uint8_t RawState() const { return mStateAndModifiers & ~Modifiers::Mask; }
+
+    uint8_t RawModifiers() const {
+      return mStateAndModifiers & Modifiers::Mask;
+    }
+
+    uint8_t mStateAndModifiers = 0;
+  };
+
   /**
    * Returns true if the current code is being executed as a result of
    * user input or keyboard input.  The former includes anything that is