diff --git a/tests/review-style-layout.e2e.test.mjs b/tests/review-style-layout.e2e.test.mjs
index fd4652d..63167e3 100644
--- a/tests/review-style-layout.e2e.test.mjs
+++ b/tests/review-style-layout.e2e.test.mjs
@@ -4,6 +4,9 @@
  */
 import assert from "node:assert/strict";
 import { createHash } from "node:crypto";
+import { mkdtemp, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
 import { test } from "node:test";
 import { firefox } from "playwright";
 import {
@@ -548,8 +551,22 @@ test(
       await routeHomeAccount(page.context());
       await login(page, "/");
       const chromium = await userIdChipGeometry(page);
-      const browser = await firefox.launch();
+      const firefoxAppData = await mkdtemp(
+          join(tmpdir(), "console-playwright-firefox-app-"),
+        ),
+        firefoxLocalAppData = await mkdtemp(
+          join(tmpdir(), "console-playwright-firefox-local-"),
+        );
+      let browser;
       try {
+        // Firefox must not inspect a developer's personal app-data directory before using its test profile.
+        browser = await firefox.launch({
+          env: {
+            ...process.env,
+            MOZ_APP_DATA: firefoxAppData,
+            MOZ_LOCAL_APP_DATA: firefoxLocalAppData,
+          },
+        });
         const context = await browser.newContext({
           viewport: { width: 1440, height: 900 },
           serviceWorkers: "block",
@@ -575,7 +592,12 @@ test(
         assert.deepEqual(blocked, [], "Firefox must stay on local origins");
         return { chromium, firefox: gecko };
       } finally {
-        await browser.close();
+        await browser?.close();
+        await Promise.all(
+          [firefoxAppData, firefoxLocalAppData].map((directory) =>
+            rm(directory, { recursive: true, force: true }),
+          ),
+        );
       }
     }),
 );