diff --git a/Userland/Libraries/LibWeb/DOM/MutationRecord.cpp b/Userland/Libraries/LibWeb/DOM/MutationRecord.cpp
index 9fe81a39b3..4474115470 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationRecord.cpp
+++ b/Userland/Libraries/LibWeb/DOM/MutationRecord.cpp
@@ -12,12 +12,12 @@
 
 namespace Web::DOM {
 
-WebIDL::ExceptionOr<JS::NonnullGCPtr<MutationRecord>> MutationRecord::create(JS::Realm& realm, DeprecatedFlyString const& type, Node const& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value)
+WebIDL::ExceptionOr<JS::NonnullGCPtr<MutationRecord>> MutationRecord::create(JS::Realm& realm, FlyString const& type, Node const& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value)
 {
     return MUST_OR_THROW_OOM(realm.heap().allocate<MutationRecord>(realm, realm, type, target, added_nodes, removed_nodes, previous_sibling, next_sibling, attribute_name, attribute_namespace, old_value));
 }
 
-MutationRecord::MutationRecord(JS::Realm& realm, DeprecatedFlyString const& type, Node const& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value)
+MutationRecord::MutationRecord(JS::Realm& realm, FlyString const& type, Node const& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value)
     : PlatformObject(realm)
     , m_type(type)
     , m_target(JS::make_handle(target))
diff --git a/Userland/Libraries/LibWeb/DOM/MutationRecord.h b/Userland/Libraries/LibWeb/DOM/MutationRecord.h
index 14c99a5826..273ce80602 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationRecord.h
+++ b/Userland/Libraries/LibWeb/DOM/MutationRecord.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/FlyString.h>
 #include <LibWeb/Bindings/PlatformObject.h>
 
 namespace Web::DOM {
@@ -15,11 +16,11 @@ class MutationRecord : public Bindings::PlatformObject {
     WEB_PLATFORM_OBJECT(MutationRecord, Bindings::PlatformObject);
 
 public:
-    static WebIDL::ExceptionOr<JS::NonnullGCPtr<MutationRecord>> create(JS::Realm&, DeprecatedFlyString const& type, Node const& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value);
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<MutationRecord>> create(JS::Realm&, FlyString const& type, Node const& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value);
 
     virtual ~MutationRecord() override;
 
-    DeprecatedFlyString const& type() const { return m_type; }
+    FlyString const& type() const { return m_type; }
     Node const* target() const { return m_target; }
     NodeList const* added_nodes() const { return m_added_nodes; }
     NodeList const* removed_nodes() const { return m_removed_nodes; }
@@ -30,12 +31,12 @@ public:
     DeprecatedString const& old_value() const { return m_old_value; }
 
 private:
-    MutationRecord(JS::Realm& realm, DeprecatedFlyString const& type, Node const& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value);
+    MutationRecord(JS::Realm& realm, FlyString const& type, Node const& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value);
 
     virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
-    DeprecatedFlyString m_type;
+    FlyString m_type;
     JS::GCPtr<Node const> m_target;
     JS::GCPtr<NodeList> m_added_nodes;
     JS::GCPtr<NodeList> m_removed_nodes;
diff --git a/Userland/Libraries/LibWeb/DOM/MutationType.cpp b/Userland/Libraries/LibWeb/DOM/MutationType.cpp
index b14516dfb2..41ec95e2c8 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationType.cpp
+++ b/Userland/Libraries/LibWeb/DOM/MutationType.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::DOM::MutationType {
 
-#define __ENUMERATE_MUTATION_TYPE(name) DeprecatedFlyString name;
+#define __ENUMERATE_MUTATION_TYPE(name) FlyString name;
 ENUMERATE_MUTATION_TYPES
 #undef __ENUMERATE_MUTATION_TYPE
 
@@ -17,7 +17,7 @@ ErrorOr<void> initialize_strings()
     static bool s_initialized = false;
     VERIFY(!s_initialized);
 
-#define __ENUMERATE_MUTATION_TYPE(name) name = #name;
+#define __ENUMERATE_MUTATION_TYPE(name) name = TRY(#name##_fly_string);
     ENUMERATE_MUTATION_TYPES
 #undef __ENUMERATE_MUTATION_TYPE
 
diff --git a/Userland/Libraries/LibWeb/DOM/MutationType.h b/Userland/Libraries/LibWeb/DOM/MutationType.h
index 709a596e30..961c306843 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationType.h
+++ b/Userland/Libraries/LibWeb/DOM/MutationType.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
-#include <AK/DeprecatedFlyString.h>
 #include <AK/Error.h>
+#include <AK/FlyString.h>
 
 namespace Web::DOM::MutationType {
 
@@ -16,7 +16,7 @@ namespace Web::DOM::MutationType {
     __ENUMERATE_MUTATION_TYPE(characterData) \
     __ENUMERATE_MUTATION_TYPE(childList)
 
-#define __ENUMERATE_MUTATION_TYPE(name) extern DeprecatedFlyString name;
+#define __ENUMERATE_MUTATION_TYPE(name) extern FlyString name;
 ENUMERATE_MUTATION_TYPES
 #undef __ENUMERATE_MUTATION_TYPE
 
diff --git a/Userland/Libraries/LibWeb/DOM/Node.cpp b/Userland/Libraries/LibWeb/DOM/Node.cpp
index 7d104ad9e7..171f74f7f2 100644
--- a/Userland/Libraries/LibWeb/DOM/Node.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Node.cpp
@@ -1390,7 +1390,7 @@ Painting::PaintableBox const* Node::paint_box() const
 }
 
 // https://dom.spec.whatwg.org/#queue-a-mutation-record
-void Node::queue_mutation_record(DeprecatedFlyString const& type, DeprecatedString attribute_name, DeprecatedString attribute_namespace, DeprecatedString old_value, JS::NonnullGCPtr<NodeList> added_nodes, JS::NonnullGCPtr<NodeList> removed_nodes, Node* previous_sibling, Node* next_sibling) const
+void Node::queue_mutation_record(FlyString const& type, DeprecatedString attribute_name, DeprecatedString attribute_namespace, DeprecatedString old_value, JS::NonnullGCPtr<NodeList> added_nodes, JS::NonnullGCPtr<NodeList> removed_nodes, Node* previous_sibling, Node* next_sibling) const
 {
     // NOTE: We defer garbage collection until the end of the scope, since we can't safely use MutationObserver* as a hashmap key otherwise.
     // FIXME: This is a total hack.
diff --git a/Userland/Libraries/LibWeb/DOM/Node.h b/Userland/Libraries/LibWeb/DOM/Node.h
index 2387894852..85d81e5a20 100644
--- a/Userland/Libraries/LibWeb/DOM/Node.h
+++ b/Userland/Libraries/LibWeb/DOM/Node.h
@@ -8,6 +8,7 @@
 
 #include <AK/Badge.h>
 #include <AK/DeprecatedString.h>
+#include <AK/FlyString.h>
 #include <AK/JsonObjectSerializer.h>
 #include <AK/RefPtr.h>
 #include <AK/TypeCasts.h>
@@ -227,7 +228,7 @@ public:
 
     void add_registered_observer(RegisteredObserver& registered_observer) { m_registered_observer_list.append(registered_observer); }
 
-    void queue_mutation_record(DeprecatedFlyString const& type, DeprecatedString attribute_name, DeprecatedString attribute_namespace, DeprecatedString old_value, JS::NonnullGCPtr<NodeList> added_nodes, JS::NonnullGCPtr<NodeList> removed_nodes, Node* previous_sibling, Node* next_sibling) const;
+    void queue_mutation_record(FlyString const& type, DeprecatedString attribute_name, DeprecatedString attribute_namespace, DeprecatedString old_value, JS::NonnullGCPtr<NodeList> added_nodes, JS::NonnullGCPtr<NodeList> removed_nodes, Node* previous_sibling, Node* next_sibling) const;
 
     // https://dom.spec.whatwg.org/#concept-shadow-including-descendant
     template<typename Callback>