[Bug]:connect_over_cdp fails on QtWebEngine with “Browser context management is not supported”

[amin-hv]

Version

1.54

Steps to reproduce

When attaching Playwright to a PyQt5 QWebEngineView (QtWebEngine) via CDP, the initial Browser.setDownloadBehavior RPC always errors out because QtWebEngine’s DevTools server doesn’t implement it. As a result chromium.connect_over_cdp(wsUrl) immediately aborts with:
Protocol error (Browser.setDownloadBehavior): Browser context management is not supported.

Steps to reproduce:

1. Launch a PyQt5 app with QTWEBENGINE_REMOTE_DEBUGGING=9222 and load one or more pages in QWebEngineView.

2. From Python, call:

browser = await playwright.chromium.connect_over_cdp("ws://127.0.0.1:9222/devtools/page/<id>")

3. Observe the above error and no attached Page objects.

Expected behavior

Playwright should skip unsupported CDP methods (like Browser.setDownloadBehavior) on attach when the server doesn’t support them, or expose an option to disable download/context management on connect.

Actual behavior

When calling await playwright.chromium.connect_over_cdp(wsUrl), Playwright immediately sends a Browser.setDownloadBehavior CDP command, which QtWebEngine rejects. The attach call then fails with:

Protocol error (Browser.setDownloadBehavior): Browser context management is not supported.
No Page objects are returned and all subsequent automation is aborted.

Additional context

Environment

▶ Playwright version: Version 1.54.0
▶ Python version: Python 3.10.18
▶ PyQt5 version: Version: 5.15.11
▶ Qt version: QMake version 3.1
▶ OS release: Ubuntu 24.04.2 LTS

[agg23]

QtWebEngine is out of scope for Playwright support. CDP is intended to talk to Chromium with all of it's functionality. If QtWebEngine forks Chromium and removes pieces, that is not Playwright's fault.