diff --git a/moli-benchmark/README.md b/moli-benchmark/README.md
index b9c76d2ed5..ddef473413 100644
--- a/moli-benchmark/README.md
+++ b/moli-benchmark/README.md
@@ -130,6 +130,9 @@ them. The runner waits for load, fonts, two animation frames, and removal of
 `crashtest` with zero subtests. An outstanding wait remains a timeout, and a
 renderer crash is reported even when the browser process stays alive.
 
+The Chrome CDP driver disables popup blocking so WPT cases can open auxiliary
+test windows without user activation, as they do under ChromeDriver.
+
 ### Cross-engine layout WPT
 
 The standalone cross-engine runner has separate layout profiles, so its
diff --git a/moli-benchmark/moli_benchmark/wpt_cross/engine.py b/moli-benchmark/moli_benchmark/wpt_cross/engine.py
index 7d86aed062..d77b6d92bf 100644
--- a/moli-benchmark/moli_benchmark/wpt_cross/engine.py
+++ b/moli-benchmark/moli_benchmark/wpt_cross/engine.py
@@ -269,6 +269,8 @@ def _chrome_command(binary: Path, port: int, tmp: Path | None) -> list[str]:
         "--no-sandbox",
         "--disable-gpu",
         "--disable-dev-shm-usage",
+        # WPT opens auxiliary test windows without user activation.
+        "--disable-popup-blocking",
         "--no-first-run",
         f"--user-data-dir={tmp}",
         f"--remote-debugging-port={port}",