Codex Desktop Browser Use blocks an explicitly allowed website

Environment

• Windows
• Codex Desktop 0.149.0-alpha.4.1
• In-app Browser / Browser Use
• Website: https://1f3d9.com
• Reproduced August 22, 2026

Summary

Codex Desktop Browser Use is blocking navigation to an explicitly allowed public website with:

net::ERR_BLOCKED_BY_CLIENT

The hostname is explicitly allowed under Settings → Browser.

This appears to be a recent regression. Browser Use successfully accessed this same website after August 13, 2026 using the same general Firefly/AI City workflow. The failure began only recently.

Reproduction

The failure occurs in two independent contexts:

1. A background scheduled task.
2. A brand-new ordinary user-created project task.

The ordinary task had:

thread_source=user

so the problem does not appear limited to scheduled/background execution or an approval_policy=never environment.

In both cases, Browser Use attempts to navigate to:

https://1f3d9.com

and receives:

net::ERR_BLOCKED_BY_CLIENT

Important isolation

The failure occurs during in-app Browser navigation, before the destination website or its MCP server is contacted.

The website itself remains publicly reachable outside this Browser Use path.

The project also has an MCP integration associated with this service, but the observed failure happens before MCP authentication or communication is attempted. This therefore does not appear to originate from the remote MCP server or its authentication mechanism.

Expected behavior

A public website explicitly configured as allowed under Settings → Browser should be navigable by Browser Use.

If another security or policy layer overrides the user-visible allowlist, the product should surface that policy and explain why navigation was denied.

Actual behavior

Browser Use rejects the navigation with:

net::ERR_BLOCKED_BY_CLIENT

despite the hostname being explicitly allowed.

Recreating the task as an ordinary user-created task does not change the result.

Regression signal

Browser Use successfully accessed this same website and workflow on August 21, 2026.

The failure was first observed and reproduced on August 22, 2026, after a Codex Desktop alpha/beta update on August 21. The currently affected environment is running 0.149.0-alpha.4.1.

This suggests a possible regression introduced by that update or an associated bundled Browser/security-policy change, rather than a longstanding incompatibility with the site.

Requested investigation

Please investigate why Browser Use now returns ERR_BLOCKED_BY_CLIENT for a hostname explicitly allowed under Settings → Browser, despite the same website and workflow working successfully the previous day.

In particular, please check whether the August 21 Codex Desktop alpha/beta update or an associated Browser/security-policy component introduced this regression.

If another policy intentionally overrides the user-visible allowlist, please expose the effective policy or blocking reason in the UI.

No source file, test, or entry point is named. Reproduce the failure in Codex Desktop 0.149.0-alpha.4.1 with https://1f3d9.com, then trace the in-app Browser navigation and effective allowlist or security policy, comparing with the previous working version. Done means an explicitly allowed site navigates successfully or the UI explains the overriding policy.