diff --git a/Libraries/LibWeb/HTML/TraversableNavigable.cpp b/Libraries/LibWeb/HTML/TraversableNavigable.cpp
index 50466d4af3..64dbad07ce 100644
--- a/Libraries/LibWeb/HTML/TraversableNavigable.cpp
+++ b/Libraries/LibWeb/HTML/TraversableNavigable.cpp
@@ -125,7 +125,11 @@ GC::Ref<TraversableNavigable> TraversableNavigable::create_a_new_top_level_trave
     traversable->m_session_history_entries.append(*initial_history_entry);
     traversable->set_has_session_history_entry_and_ready_for_navigation();
 
-    // FIXME: 10. If opener is non-null, then legacy-clone a traversable storage shed given opener's top-level traversable and traversable. [STORAGE]
+    // 10. If opener is non-null, then legacy-clone a traversable storage shed given opener's top-level traversable and traversable. [STORAGE]
+    if (opener) {
+        auto opener_traversable = opener->top_level_traversable();
+        traversable->storage_shed().legacy_clone(opener_traversable->storage_shed(), page);
+    }
 
     // 11. Append traversable to the user agent's top-level traversable set.
     user_agent_top_level_traversable_set().set(traversable);
diff --git a/Libraries/LibWeb/StorageAPI/StorageBottle.cpp b/Libraries/LibWeb/StorageAPI/StorageBottle.cpp
index 644c2b867c..c4189a3c60 100644
--- a/Libraries/LibWeb/StorageAPI/StorageBottle.cpp
+++ b/Libraries/LibWeb/StorageAPI/StorageBottle.cpp
@@ -183,4 +183,9 @@ void SessionStorageBottle::remove(String const& key)
     m_map.remove(key);
 }
 
+void SessionStorageBottle::copy_map_from(SessionStorageBottle const& other)
+{
+    m_map = other.m_map;
+}
+
 }
diff --git a/Libraries/LibWeb/StorageAPI/StorageBottle.h b/Libraries/LibWeb/StorageAPI/StorageBottle.h
index 9451cf1f14..584b39f3c5 100644
--- a/Libraries/LibWeb/StorageAPI/StorageBottle.h
+++ b/Libraries/LibWeb/StorageAPI/StorageBottle.h
@@ -97,6 +97,8 @@ public:
     virtual void clear() override;
     virtual void remove(String const&) override;
 
+    void copy_map_from(SessionStorageBottle const&);
+
 private:
     explicit SessionStorageBottle(Optional<u64> quota)
         : StorageBottle(quota)
diff --git a/Libraries/LibWeb/StorageAPI/StorageShed.cpp b/Libraries/LibWeb/StorageAPI/StorageShed.cpp
index 812abfcaad..d923e09997 100644
--- a/Libraries/LibWeb/StorageAPI/StorageShed.cpp
+++ b/Libraries/LibWeb/StorageAPI/StorageShed.cpp
@@ -4,9 +4,11 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/TypeCasts.h>
 #include <LibGC/Heap.h>
 #include <LibWeb/HTML/Scripting/Environments.h>
 #include <LibWeb/HTML/Window.h>
+#include <LibWeb/StorageAPI/StorageBottle.h>
 #include <LibWeb/StorageAPI/StorageShed.h>
 
 namespace Web::StorageAPI {
@@ -38,4 +40,28 @@ GC::Ptr<StorageShelf> StorageShed::obtain_a_storage_shelf(HTML::EnvironmentSetti
     });
 }
 
+// https://storage.spec.whatwg.org/#legacy-clone-a-traversable-storage-shed
+// To legacy-clone a traversable storage shed, given a traversable navigable A and a traversable navigable B, run these steps:
+void StorageShed::legacy_clone(StorageShed const& a_storage_shed, GC::Ref<Page> page)
+{
+    // 1. For each key → shelf of A’s storage shed:
+    for (auto const& [key, shelf] : a_storage_shed.m_data) {
+
+        // 1. Let newShelf be the result of running create a storage shelf with "session".
+        auto new_shelf = StorageShelf::create(heap(), page, key, StorageType::Session);
+
+        // 2. Set newShelf’s bucket map["default"]'s bottle map["sessionStorage"]'s map to a clone of shelf’s bucket map["default"]'s bottle map["sessionStorage"]'s map.
+        auto& shelf_bucket = *shelf->bucket_map().get("default"sv).value();
+        auto& new_shelf_bucket = *new_shelf->bucket_map().get("default"sv).value();
+
+        auto const& shelf_bottle = *shelf_bucket.bottle_map()[to_underlying(StorageEndpointType::SessionStorage)];
+        auto& new_shelf_bottle = *new_shelf_bucket.bottle_map()[to_underlying(StorageEndpointType::SessionStorage)];
+
+        as<SessionStorageBottle>(new_shelf_bottle).copy_map_from(static_cast<SessionStorageBottle const&>(shelf_bottle));
+
+        // 3. Set B’s storage shed[key] to newShelf.
+        m_data.set(key, new_shelf);
+    }
+}
+
 }
diff --git a/Libraries/LibWeb/StorageAPI/StorageShed.h b/Libraries/LibWeb/StorageAPI/StorageShed.h
index 9bcf643b04..41966960f9 100644
--- a/Libraries/LibWeb/StorageAPI/StorageShed.h
+++ b/Libraries/LibWeb/StorageAPI/StorageShed.h
@@ -25,6 +25,7 @@ public:
     static GC::Ref<StorageShed> create(GC::Heap& heap) { return heap.allocate<StorageShed>(); }
 
     GC::Ptr<StorageShelf> obtain_a_storage_shelf(HTML::EnvironmentSettingsObject&, StorageType);
+    void legacy_clone(StorageShed const&, GC::Ref<Page>);
 
     virtual void visit_edges(GC::Cell::Visitor& visitor) override;
 
diff --git a/Tests/LibWeb/TestConfig.ini b/Tests/LibWeb/TestConfig.ini
index f257414c04..40bce6b484 100644
--- a/Tests/LibWeb/TestConfig.ini
+++ b/Tests/LibWeb/TestConfig.ini
@@ -32,6 +32,7 @@ Text/input/wpt-import/html/syntax/parsing/unclosed-svg-script.html
 ; These tests require cross-origin iframe access to succeed.
 Text/input/wpt-import/webstorage/event_session_oldvalue.html
 Text/input/wpt-import/webstorage/event_session_storagearea.html
+Text/input/wpt-import/webstorage/storage_session_window_open.window.html
 Text/input/navigation/navigation-navigate.html
 Text/input/navigation/location-reload-fetch.html
 Text/input/HTML/session-storage-event-fired-to-lazy-window.html
diff --git a/Tests/LibWeb/Text/expected/wpt-import/webstorage/storage_session_window_open.window.txt b/Tests/LibWeb/Text/expected/wpt-import/webstorage/storage_session_window_open.window.txt
new file mode 100644
index 0000000000..d6a98cbd25
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/webstorage/storage_session_window_open.window.txt
@@ -0,0 +1,6 @@
+Harness status: OK
+
+Found 1 tests
+
+1 Pass
+Pass	A new window to make sure there is a copy of the previous window's sessionStorage, and that they diverge after a change
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/webstorage/resources/storage_session_window_open_second.html b/Tests/LibWeb/Text/input/wpt-import/webstorage/resources/storage_session_window_open_second.html
new file mode 100644
index 0000000000..2eeff0b865
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/webstorage/resources/storage_session_window_open_second.html
@@ -0,0 +1,41 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>WebStorage Test: sessionStorage - second page</title>
+</head>
+<body>
+<script>
+
+var storage = window.sessionStorage;
+
+var assertions = [];
+
+assertions.push({
+    actual: storage.getItem("FOO"),
+    expected: "BAR",
+    message: "storage.getItem('FOO')"
+});
+
+storage.setItem("FOO", "BAR-NEWWINDOW");
+
+assertions.push({
+    actual: storage.getItem("FOO"),
+    expected: "BAR-NEWWINDOW",
+    message: "value for FOO after changing"
+});
+assertions.push({
+    actual: window.opener.sessionStorage.getItem("FOO"),
+    expected: "BAR",
+    message: "value for FOO in my opening window"
+});
+assertions.push({
+    actual: storage.getItem("BAZ"),
+    expected: null,
+    message: "value for BAZ set after window.open(), is not set in new window"
+});
+
+window.opener.postMessage(assertions, '*');
+
+</script>
+</body>
+</html>
diff --git a/Tests/LibWeb/Text/input/wpt-import/webstorage/storage_session_window_open.window.html b/Tests/LibWeb/Text/input/wpt-import/webstorage/storage_session_window_open.window.html
new file mode 100644
index 0000000000..a6d935f5b1
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/webstorage/storage_session_window_open.window.html
@@ -0,0 +1,8 @@
+<!doctype html>
+<meta charset=utf-8>
+
+<script src="../resources/testharness.js"></script>
+<script src="../resources/testharnessreport.js"></script>
+
+<div id=log></div>
+<script src="../webstorage/storage_session_window_open.window.js"></script>
diff --git a/Tests/LibWeb/Text/input/wpt-import/webstorage/storage_session_window_open.window.js b/Tests/LibWeb/Text/input/wpt-import/webstorage/storage_session_window_open.window.js
new file mode 100644
index 0000000000..83d4447017
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/webstorage/storage_session_window_open.window.js
@@ -0,0 +1,17 @@
+async_test(function(t) {
+
+    var storage = window.sessionStorage;
+    storage.clear();
+
+    storage.setItem("FOO", "BAR");
+    var win = window.open("resources/storage_session_window_open_second.html");
+    storage.setItem("BAZ", "QUX");
+    window.addEventListener('message', t.step_func(function(e) {
+        e.data.forEach(t.step_func(function(assertion) {
+            assert_equals(assertion.actual, assertion.expected, assertion.message);
+        }));
+        win.close();
+        t.done();
+    }));
+
+}, "A new window to make sure there is a copy of the previous window's sessionStorage, and that they diverge after a change");