diff --git a/Libraries/LibWeb/DOM/Document.cpp b/Libraries/LibWeb/DOM/Document.cpp
index 3d0261f25ee97..4c0c85478424a 100644
--- a/Libraries/LibWeb/DOM/Document.cpp
+++ b/Libraries/LibWeb/DOM/Document.cpp
@@ -5781,10 +5781,16 @@ void Document::unload(GC::Ptr<Document>)
         // 2. Fire a page transition event named pagehide at oldDocument's relevant global object with oldDocument's
         //    salvageable state.
         HTML::relevant_window(*this).fire_a_page_transition_event(HTML::EventNames::pagehide, m_salvageable);
+    }
 
-        // 3. Update the visibility state of oldDocument to "hidden".
+    // 3. Update the visibility state of oldDocument to "hidden".
+    // AD-HOC: Violate the spec requirement for the page to be showing (in the spec, this step is a substep of step 10
+    //         above — not a sibling step) and instead do this for any page ready for post-load tasks; e.g., the initial
+    //         about:blank of a never-navigated child. Gecko/WebKit/Blink consider such pages to be completely loaded —
+    //         and update their visibility state when unloading them.
+    //         See https://github.com/whatwg/html/issues/12288
+    if (m_ready_for_post_load_tasks)
         update_the_visibility_state(HTML::VisibilityState::Hidden);
-    }
 
     // FIXME: 11. If unloadTimingInfo is not null, then set unloadTimingInfo's unload event start time to the current high
     //     resolution time given newDocument's relevant global object, coarsened given oldDocument's relevant settings
diff --git a/Libraries/LibWeb/HTML/NavigableContainer.cpp b/Libraries/LibWeb/HTML/NavigableContainer.cpp
index 6992df0b8f5ae..9993008afe4da 100644
--- a/Libraries/LibWeb/HTML/NavigableContainer.cpp
+++ b/Libraries/LibWeb/HTML/NavigableContainer.cpp
@@ -311,7 +311,7 @@ void NavigableContainer::destroy_the_child_navigable()
 
     // Not in the spec:
     // Setting container's content navigable makes document *not* be "fully active".
-    // Therefore, it is moved to run in afterAllDestruction callback of "destroy a document and its descendants"
+    // Therefore, it is moved to run in the after-all-unloads callback of "unload a document and its descendants"
     // when all queued tasks are done.
     // "Has been destroyed" flag is used instead to check whether navigable is already destroyed.
     auto& local_navigable = as<LocalNavigable>(*navigable);
@@ -365,14 +365,21 @@ void NavigableContainer::destroy_the_child_navigable()
     });
 
     // 5. Destroy a document and its descendants given navigable's active document.
+    // AD-HOC: We unload the document and its descendants, instead of just destroying. Unloading fires pagehide at the
+    //         document's relevant global object, updates its visibility state to "hidden" (firing visibilitychange),
+    //         and fires unload — before destroying the document. The spec as written would leave a removed container's
+    //         content documents reporting a "visible" visibility state — with no events fired; Gecko/WebKit/Blink all
+    //         fire those events, and report such documents as hidden. This also means starting a view transition in a
+    //         removed document skips the transition — since startViewTransition() skips transitions for hidden docs.
+    //         See https://github.com/whatwg/html/issues/12288
     // AD-HOC: The spec assumes the active document is non-null here, but during an ancestor
     //         unload the child documents are unloaded (and destroyed) before the ancestor's
     //         pagehide fires. If that pagehide handler then removes a subtree containing this
     //         container, we reach step 5 with navigable's active document already null. We
-    //         treat the destroy step as a no-op in that case and proceed with the remaining
+    //         treat the unload step as a no-op in that case and proceed with the remaining
     //         post-destruction cleanup.
     if (auto active_document = local_navigable.active_document())
-        active_document->destroy_a_document_and_its_descendants(after_document_destruction);
+        active_document->unload_a_document_and_its_descendants({}, after_document_destruction);
     else
         after_document_destruction->function()();
 }
diff --git a/Tests/LibWeb/TestConfig.ini b/Tests/LibWeb/TestConfig.ini
index a0468ff85b32d..f3300dbef9a2e 100644
--- a/Tests/LibWeb/TestConfig.ini
+++ b/Tests/LibWeb/TestConfig.ini
@@ -272,6 +272,7 @@ Text/input/wpt-import/html/webappapis/dynamic-markup-insertion/opening-the-input
 Text/input/wpt-import/html/webappapis/scripting/processing-model-2/integration-with-the-javascript-job-queue/promise-job-entry-different-function-realm.html
 Text/input/wpt-import/navigation-api/navigation-methods/reload-state-and-info.html
 Text/input/wpt-import/navigation-api/navigation-methods/reload-state-undefined.html
+Text/input/wpt-import/page-visibility/iframe-unload.html
 Text/input/wpt-import/page-visibility/test_child_document.html
 Text/input/wpt-import/html/canvas/offscreen/text/2d.text.font.default.worker.html
 Text/input/wpt-import/html/canvas/offscreen/text/2d.text.font.parse.basic.worker.html
diff --git a/Tests/LibWeb/Text/expected/HTML/iframe-removal-sets-visibility-state-hidden.txt b/Tests/LibWeb/Text/expected/HTML/iframe-removal-sets-visibility-state-hidden.txt
new file mode 100644
index 0000000000000..e4e4b3476af04
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/HTML/iframe-removal-sets-visibility-state-hidden.txt
@@ -0,0 +1,5 @@
+before removal: visible
+pagehide fired: persisted=false
+visibilitychange fired: hidden
+unload fired
+after removal: hidden
diff --git a/Tests/LibWeb/Text/expected/HTML/view-transition-in-removed-iframe-is-skipped.txt b/Tests/LibWeb/Text/expected/HTML/view-transition-in-removed-iframe-is-skipped.txt
new file mode 100644
index 0000000000000..7e3d6b0790529
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/HTML/view-transition-in-removed-iframe-is-skipped.txt
@@ -0,0 +1,2 @@
+after removal: hidden
+ready rejected: InvalidStateError
diff --git a/Tests/LibWeb/Text/expected/wpt-import/page-visibility/iframe-unload.txt b/Tests/LibWeb/Text/expected/wpt-import/page-visibility/iframe-unload.txt
new file mode 100644
index 0000000000000..39505f315f43a
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/page-visibility/iframe-unload.txt
@@ -0,0 +1,6 @@
+Harness status: OK
+
+Found 1 tests
+
+1 Pass
+Pass	visibilitychange fires on unload with iframes
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/HTML/iframe-removal-sets-visibility-state-hidden.html b/Tests/LibWeb/Text/input/HTML/iframe-removal-sets-visibility-state-hidden.html
new file mode 100644
index 0000000000000..e21f50d05f68e
--- /dev/null
+++ b/Tests/LibWeb/Text/input/HTML/iframe-removal-sets-visibility-state-hidden.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<script src="../include.js"></script>
+<script>
+    // Removing an iframe must unload its content document: pagehide fires at the content window, the content document's
+    // visibility state becomes "hidden" (firing visibilitychange), and "unload" fires. See #9893.
+    asyncTest(async (done) => {
+        const iframe = document.createElement("iframe");
+        iframe.srcdoc = "<p>child</p>";
+        await new Promise(resolve => {
+            iframe.onload = resolve;
+            document.body.appendChild(iframe);
+        });
+
+        const childDocument = iframe.contentDocument;
+        const childWindow = iframe.contentWindow;
+        println(`before removal: ${childDocument.visibilityState}`);
+
+        childWindow.addEventListener("pagehide", event => {
+            println(`pagehide fired: persisted=${event.persisted}`);
+        });
+        childDocument.addEventListener("visibilitychange", () => {
+            println(`visibilitychange fired: ${childDocument.visibilityState}`);
+        });
+        childWindow.addEventListener("unload", () => {
+            println("unload fired");
+            setTimeout(() => {
+                println(`after removal: ${childDocument.visibilityState}`);
+                done();
+            }, 0);
+        });
+
+        iframe.remove();
+    });
+</script>
diff --git a/Tests/LibWeb/Text/input/HTML/view-transition-in-removed-iframe-is-skipped.html b/Tests/LibWeb/Text/input/HTML/view-transition-in-removed-iframe-is-skipped.html
new file mode 100644
index 0000000000000..24560868c3b77
--- /dev/null
+++ b/Tests/LibWeb/Text/input/HTML/view-transition-in-removed-iframe-is-skipped.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<script src="../include.js"></script>
+<script>
+    // A view transition started in the document of a removed iframe must be skipped with an InvalidStateError — because
+    // the document's visibility state is "hidden" after removal. See #9893.
+    asyncTest(async (done) => {
+        const iframe = document.createElement("iframe");
+        iframe.srcdoc = "<p>child</p>";
+        await new Promise(r => { iframe.onload = r; document.body.appendChild(iframe); });
+        const childDocument = iframe.contentDocument;
+        const hidden = new Promise(resolve => childDocument.addEventListener("visibilitychange", resolve, { once: true }));
+        iframe.remove();
+        await hidden;
+        println(`after removal: ${childDocument.visibilityState}`);
+        const transition = childDocument.startViewTransition(() => {});
+        const result = await Promise.race([
+            transition.ready.then(() => "ready resolved", (e) => `ready rejected: ${e.name}`),
+            new Promise(r => setTimeout(() => r("ready never settled (hang)"), 1500)),
+        ]);
+        println(result);
+        done();
+    });
+</script>
diff --git a/Tests/LibWeb/Text/input/wpt-import/page-visibility/iframe-unload.html b/Tests/LibWeb/Text/input/wpt-import/page-visibility/iframe-unload.html
new file mode 100644
index 0000000000000..5d4bed14ee02d
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/page-visibility/iframe-unload.html
@@ -0,0 +1,49 @@
+<html>
+<title>visibilitychange fires on unload with iframes</title>
+<script src="../resources/testharness.js"></script>
+<script src="../resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+
+var frameDocs = [];
+var docsLoaded = 0;
+var numFrames = 3;
+
+var ast = new async_test("visibilitychange fires on unload with iframes");
+
+function startTest() {
+  if (++docsLoaded < numFrames)
+    return;
+
+  ast.step(function () {
+    frameDocs.push(window[0].document);
+    frameDocs.push(window[0][0].document);
+    frameDocs.push(window[0][1].document);
+
+    for (var i = 0; i < frameDocs.length; ++i) {
+      frameDocs[i].addEventListener(
+          "visibilitychange",
+          onVisibilityChange.bind(null, i), false);
+    }
+
+    document.body.removeChild(document.getElementById("frame1"));
+  });
+}
+
+var checkedFrames = 0;
+
+function onVisibilityChange(i) {
+  ast.step(function () {
+    assert_equals(frameDocs[i].visibilityState, "hidden");
+  });
+  if (++checkedFrames >= numFrames) {
+    ast.done();
+  }
+}
+
+
+
+</script>
+<iframe id="frame1" src="resources/iframe-with-subframes.html"></iframe>
+</body>
+</html>
diff --git a/Tests/LibWeb/Text/input/wpt-import/page-visibility/resources/iframe-with-subframes.html b/Tests/LibWeb/Text/input/wpt-import/page-visibility/resources/iframe-with-subframes.html
new file mode 100644
index 0000000000000..febb954369995
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/page-visibility/resources/iframe-with-subframes.html
@@ -0,0 +1,6 @@
+<html>
+<body onload="parent.startTest()">
+<iframe id="subIframe1" onload="parent.parent.startTest()"></iframe>
+<iframe id="subIframe2" onload="parent.parent.startTest()"></iframe>
+</body>
+</html>