diff --git a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
index 722e3df0c5b..55165338ff1 100644
--- a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
+++ b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
@@ -96,6 +96,33 @@ bool MouseEvent::get_modifier_state(String const& key_arg) const
     return false;
 }
 
+// https://w3c.github.io/uievents/#dom-mouseevent-initmouseevent
+void MouseEvent::init_mouse_event(String const& type, bool bubbles, bool cancelable, HTML::Window* view, WebIDL::Long detail, WebIDL::Long screen_x, WebIDL::Long screen_y, WebIDL::Long client_x, WebIDL::Long client_y, bool ctrl_key, bool alt_key, bool shift_key, bool meta_key, WebIDL::Short button, DOM::EventTarget* related_target)
+{
+    // Initializes attributes of a MouseEvent object. This method has the same behavior as UIEvent.initUIEvent().
+
+    // 1. If this’s dispatch flag is set, then return.
+    if (dispatched())
+        return;
+
+    // 2. Initialize this with type, bubbles, and cancelable.
+    initialize_event(type, bubbles, cancelable);
+
+    // Implementation Defined: Initialise other values.
+    m_view = view;
+    m_detail = detail;
+    m_screen_x = screen_x;
+    m_screen_y = screen_y;
+    m_client_x = client_x;
+    m_client_y = client_y;
+    m_ctrl_key = ctrl_key;
+    m_shift_key = shift_key;
+    m_alt_key = alt_key;
+    m_meta_key = meta_key;
+    m_button = button;
+    m_related_target = related_target;
+}
+
 // https://www.w3.org/TR/uievents/#dom-mouseevent-button
 static i16 determine_button(unsigned mouse_button)
 {
diff --git a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
index 50b568f7f1e..a4b9ec9b973 100644
--- a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
+++ b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
@@ -68,6 +68,8 @@ public:
 
     virtual u32 which() const override { return m_button + 1; }
 
+    void init_mouse_event(String const& type, bool bubbles, bool cancelable, HTML::Window* view, WebIDL::Long detail, WebIDL::Long screen_x, WebIDL::Long screen_y, WebIDL::Long client_x, WebIDL::Long client_y, bool ctrl_key, bool alt_key, bool shift_key, bool meta_key, WebIDL::Short button, DOM::EventTarget* related_target);
+
 protected:
     MouseEvent(JS::Realm&, FlyString const& event_name, MouseEventInit const& event_init, double page_x, double page_y, double offset_x, double offset_y);
 
diff --git a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl
index fb589ebbf7d..e7b5985b000 100644
--- a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl
+++ b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl
@@ -32,6 +32,9 @@ interface MouseEvent : UIEvent {
     readonly attribute EventTarget? relatedTarget;
 
     boolean getModifierState(DOMString keyArg);
+
+    // https://w3c.github.io/uievents/#dom-mouseevent-initmouseevent
+    undefined initMouseEvent(DOMString typeArg, optional boolean bubblesArg = false, optional boolean cancelableArg = false, optional Window? viewArg = null, optional long detailArg = 0, optional long screenXArg = 0, optional long screenYArg = 0, optional long clientXArg = 0, optional long clientYArg = 0, optional boolean ctrlKeyArg = false, optional boolean altKeyArg = false, optional boolean shiftKeyArg = false, optional boolean metaKeyArg = false, optional short buttonArg = 0, optional EventTarget? relatedTargetArg = null);
 };
 
 // https://w3c.github.io/uievents/#idl-mouseeventinit