diff --git a/tests/e2e/README.md b/tests/e2e/README.md
index b15a2c1..a8dc951 100644
--- a/tests/e2e/README.md
+++ b/tests/e2e/README.md
@@ -50,6 +50,21 @@ reads as a broken fixture instead of a scoring regression.
 | `background-loop.html` | Silent looping hero must lose despite being the largest |
 | `multi-player.html` | Between equal players, the playing one wins |
 | `sourceless.html` | A large `<video>` with no source can never be the player |
+| `nested-frame.html` | Player two frame levels down |
+| `reloading-frame.html` | Frame that swaps its document, with no mutation in the top one |
+
+## Benchmark
+
+`bench-finder.mjs` is not a spec, because timings are machine dependent and
+would only add noise to CI. Run it by hand when the finder changes:
+
+```bash
+node tests/e2e/fixture-server.mjs 4173 & node tests/e2e/bench-finder.mjs
+```
+
+It measures the shipped finder (lifted from `content.js`) against the
+pre-v3.1.0 formula, which is transcribed inside the script since that code no
+longer exists in the tree.
 
 ## Regenerating the media
 
diff --git a/tests/e2e/bench-finder.mjs b/tests/e2e/bench-finder.mjs
new file mode 100644
index 0000000..8552b7f
--- /dev/null
+++ b/tests/e2e/bench-finder.mjs
@@ -0,0 +1,76 @@
+#!/usr/bin/env node
+/**
+ * Measures findVideo() on a page loaded with same-origin frames.
+ *
+ * Not a spec: timings are machine dependent and would only add noise to CI.
+ * Run it by hand when the finder changes:
+ *
+ *   node tests/e2e/fixture-server.mjs 4173 &
+ *   node tests/e2e/bench-finder.mjs
+ *
+ * The measured implementation is the shipped one, lifted out of content.js by
+ * the same helper the specs use. The pre-v3.1.0 formula it is compared against
+ * is transcribed here, since that code no longer exists in the tree.
+ */
+import { chromium } from '@playwright/test';
+import { buildVideoFinderScript } from './helpers/content-source.mjs';
+
+const url = process.env.KOALA_E2E_URL || 'http://localhost:4173/pages/ad-frame.html';
+const FRAMES = Number(process.env.KOALA_BENCH_FRAMES || 40);
+const CALLS = Number(process.env.KOALA_BENCH_CALLS || 200);
+
+const browser = await chromium.launch({ args: ['--autoplay-policy=no-user-gesture-required'] });
+const page = await browser.newPage();
+await page.goto(url);
+await page.waitForFunction(() => window.__fixtureReady === true);
+await page.addScriptTag({ content: buildVideoFinderScript() });
+
+const result = await page.evaluate(({ frames, calls }) => {
+    // Pre-v3.1.0 scoring, kept only as the baseline for this measurement.
+    function findVideoLegacy(root = document) {
+        const candidates = window.__koalaCollect(root);
+        if (!candidates.length) return null;
+        if (candidates.length === 1) return candidates[0];
+        let best = null;
+        let bestScore = -1;
+        for (const v of candidates) {
+            if (v.tagName !== 'VIDEO') continue;
+            const area = (v.videoWidth || v.offsetWidth || 0) * (v.videoHeight || v.offsetHeight || 0);
+            const score = area + (v.muted ? 0 : 100000)
+                + (v.duration && isFinite(v.duration) ? v.duration : 0) * 100;
+            if (score > bestScore) { bestScore = score; best = v; }
+        }
+        return best;
+    }
+    window.__koalaCollect = (root) => window.collectVideoCandidates(root, 0, []);
+
+    const holder = document.createElement('div');
+    document.body.appendChild(holder);
+    for (let i = 0; i < frames; i++) {
+        const frame = document.createElement('iframe');
+        frame.style.display = 'none';
+        holder.appendChild(frame);
+    }
+
+    // globalThis keeps this readable to a Node-configured linter: the body runs
+    // in the page, where performance is a global.
+    const clock = globalThis.performance;
+    const bench = (fn) => {
+        for (let i = 0; i < 20; i++) fn();
+        const start = clock.now();
+        for (let i = 0; i < calls; i++) fn();
+        return (clock.now() - start) / calls;
+    };
+
+    const current = bench(() => window.__koalaFindVideo());
+    const legacy = bench(() => findVideoLegacy());
+    const frameCount = document.querySelectorAll('iframe, frame').length;
+    holder.remove();
+    return { frameCount, current, legacy };
+}, { frames: FRAMES, calls: CALLS });
+
+console.log(`frames on page:      ${result.frameCount}`);
+console.log(`shipped findVideo:   ${result.current.toFixed(3)} ms/call`);
+console.log(`pre-v3.1.0 formula:  ${result.legacy.toFixed(3)} ms/call`);
+
+await browser.close();
diff --git a/tests/e2e/detection.spec.mjs b/tests/e2e/detection.spec.mjs
index bd47118..b3dae48 100644
--- a/tests/e2e/detection.spec.mjs
+++ b/tests/e2e/detection.spec.mjs
@@ -10,6 +10,7 @@ import { buildVideoFinderScript } from './helpers/content-source.mjs';
 const SCENARIOS = [
     { page: 'simple-player.html', expected: 'player', what: 'the only visible player' },
     { page: 'iframe-player.html', expected: 'framed-player', what: 'a player inside a same-origin frame' },
+    { page: 'nested-frame.html', expected: 'framed-player', what: 'a player two frame levels down' },
     { page: 'shadow-player.html', expected: 'shadow-player', what: 'a player inside a shadow root over a light-DOM teaser' },
     { page: 'muted-player.html', expected: 'player', what: 'the only player even when muted' },
     { page: 'hidden-preload.html', expected: 'player', what: 'the visible player over a hidden higher-resolution preload' },
diff --git a/tests/e2e/extension.spec.mjs b/tests/e2e/extension.spec.mjs
index ebcf304..f7918ef 100644
--- a/tests/e2e/extension.spec.mjs
+++ b/tests/e2e/extension.spec.mjs
@@ -103,6 +103,62 @@ test('reinjects after the target tab navigates', async ({ context, extensionId,
     ).toBe('true');
 });
 
+test('re-attaches after the player frame swaps its document', async ({ context, extensionId, baseURL }) => {
+    const url = `${baseURL}/pages/reloading-frame.html`;
+    const page = await context.newPage();
+    await page.goto(url);
+    await page.waitForFunction(() => window.__fixtureReady === true);
+    await selectTargetTab(context, extensionId, url);
+
+    await expect.poll(() => page.evaluate(() => {
+        const video = document.querySelector('iframe').contentDocument.getElementById('framed-player');
+        return video ? video.dataset.koalaAttached : null;
+    })).toBe('true');
+
+    // Navigating the frame replaces its document without touching the top one,
+    // so nothing but a load hook on the frame can notice the new player.
+    await page.evaluate(() => {
+        document.querySelector('iframe').src = 'frames/player-frame-2.html';
+    });
+
+    await expect.poll(
+        () => page.evaluate(() => {
+            const video = document.querySelector('iframe').contentDocument.getElementById('framed-player-2');
+            return video ? video.dataset.koalaAttached : null;
+        }),
+        { message: 'the content script should follow the frame to its new document' }
+    ).toBe('true');
+});
+
+test('re-attaches when a nested player frame swaps its document', async ({ context, extensionId, baseURL }) => {
+    const url = `${baseURL}/pages/nested-frame.html`;
+    const page = await context.newPage();
+    await page.goto(url);
+    await page.waitForFunction(() => window.__fixtureReady === true);
+    await selectTargetTab(context, extensionId, url);
+
+    const innerVideo = (id) => page.evaluate((videoId) => {
+        const outer = document.querySelector('iframe').contentDocument;
+        const inner = outer.querySelector('iframe').contentDocument;
+        const video = inner.getElementById(videoId);
+        return video ? video.dataset.koalaAttached : null;
+    }, id);
+
+    await expect.poll(() => innerVideo('framed-player')).toBe('true');
+
+    // The reloading frame sits at depth two. A load hook that only covers
+    // top-level frames would never fire for it.
+    await page.evaluate(() => {
+        const outer = document.querySelector('iframe').contentDocument;
+        outer.querySelector('iframe').src = 'player-frame-2.html';
+    });
+
+    await expect.poll(
+        () => innerVideo('framed-player-2'),
+        { message: 'a frame two levels down should be watched for reloads too' }
+    ).toBe('true');
+});
+
 function FRAMED_VIDEO_PAUSED() {
     return document.querySelector('iframe').contentDocument.querySelector('video').paused;
 }
diff --git a/tests/e2e/fixtures/pages/frames/outer-frame.html b/tests/e2e/fixtures/pages/frames/outer-frame.html
new file mode 100644
index 0000000..57f6a85
--- /dev/null
+++ b/tests/e2e/fixtures/pages/frames/outer-frame.html
@@ -0,0 +1,7 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>Outer</title>
+<style>body { margin: 0 }</style>
+<!-- Wrapper frame with no video of its own: the player sits one level deeper,
+     so anything that only walks the top document's frames misses it. -->
+<iframe class="inner_player" width="860" height="490" src="player-frame.html"></iframe>
diff --git a/tests/e2e/fixtures/pages/frames/player-frame-2.html b/tests/e2e/fixtures/pages/frames/player-frame-2.html
new file mode 100644
index 0000000..83cd604
--- /dev/null
+++ b/tests/e2e/fixtures/pages/frames/player-frame-2.html
@@ -0,0 +1,7 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>V2</title>
+<style>body { margin: 0 }</style>
+<!-- The frame's second server/quality choice: a different element, so
+     re-attaching to it is distinguishable from staying on the old one. -->
+<video id="framed-player-2" data-expected width="854" height="480" controls src="../../media/player-1080p-30s.mp4"></video>
diff --git a/tests/e2e/fixtures/pages/nested-frame.html b/tests/e2e/fixtures/pages/nested-frame.html
new file mode 100644
index 0000000..49ef81d
--- /dev/null
+++ b/tests/e2e/fixtures/pages/nested-frame.html
@@ -0,0 +1,6 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>Nested player frame</title>
+<h1>Player two frame levels down</h1>
+<iframe class="outer_frame" width="870" height="500" src="frames/outer-frame.html"></iframe>
+<script src="ready.js"></script>
diff --git a/tests/e2e/fixtures/pages/reloading-frame.html b/tests/e2e/fixtures/pages/reloading-frame.html
new file mode 100644
index 0000000..f806557
--- /dev/null
+++ b/tests/e2e/fixtures/pages/reloading-frame.html
@@ -0,0 +1,9 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>Reloading player frame</title>
+<h1>Player frame that swaps its document, like a server or quality switch</h1>
+<!-- Nothing in the top document changes when the frame navigates, so the top
+     document's MutationObserver never fires. Only a load hook on the frame can
+     notice, which is exactly what this fixture pins down. -->
+<iframe class="player_frame" width="860" height="490" src="frames/player-frame.html"></iframe>
+<script src="ready.js"></script>