[BUG] Claude Desktop App causes taskmgr.exe crash and Firefox history lock on Windows 10

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Hello Anthropic Support Team,

I would like to report a reproducible bug that occurred on two separate devices after installing the Claude Desktop App on Windows 10.

---

AFFECTED SYSTEMS

• Device 1: Windows 10, Build 10.0.19041
• Device 2: Windows 10, Build 10.0.19041
• Claude Desktop App: latest version

---

ISSUE 1: Task Manager crashes (APPCRASH)

After installing the Claude Desktop App, the Windows Task Manager crashes reproducibly in the advanced view when clicking on any element.

Error details from the Windows Event Log:

• Event Name: APPCRASH
• Error Code (P7): c0000005 (Access Violation)
• Affected file: taskmgr.exe v10.0.19041.6280
• Crash offset: 0x000748a1
• Fault bucket: 1824744983326319240, Type 4

Notably, the Sysinternals Process Explorer continues to run without issues, as it uses its own kernel drivers. The fault is therefore specific to the data path used by taskmgr.exe — likely influenced by a hook or process introduced by the Claude Desktop App.

---

ISSUE 2: Firefox cannot access its history database

After installation, Firefox displays an error on startup stating that the history database is already in use by another process. The SQLite file (places.sqlite) appears to be exclusively locked by the Claude Desktop App and is not properly released when the app is closed.

---

REPRODUCTION STEPS

1. Install the Claude Desktop App on Windows 10
2. Open Task Manager → switch to advanced view → click any element → crash occurs
3. Launch Firefox → error message regarding the history database appears

After uninstalling the Claude Desktop App and restarting: both issues are immediately resolved. The correlation has been confirmed on two independent devices and is clearly reproducible.

---

SUSPECTED ROOT CAUSE

The app appears to actively access Firefox profile data via the MCP browser connector and opens system resources that are not properly released when the app is closed (resource leak). This results in both the SQLite lock on the Firefox history database and — possibly via a hook or performance counter interference — the crash of taskmgr.exe.

---

I am available for follow-up questions and can provide additional diagnostic data (dump files, event logs) upon request.

Kind regards,
Rene

What Should Happen?

The Claude Desktop App appears to install a background process or service that actively monitors and accesses browser profile data — likely as part of its MCP (Model Context Protocol) browser integration or the "Claude in Chrome" connector.
The following behavior is suspected:

1. Exclusive file locking (Firefox)

The app opens Firefox's SQLite history database (places.sqlite) with an exclusive lock and does not release it when the app is closed or minimized. This prevents Firefox from accessing its own database on startup.

1. System-level hooking (Task Manager crash)

The app appears to register a hook, DLL injection, or performance counter that interferes with the data path used by taskmgr.exe. When the Task Manager attempts to read process information in advanced view, it triggers an Access Violation (c0000005) at offset 0x000748a1 — suggesting it reads from a memory address that has been altered or invalidated by the Claude app's process. Sysinternals Process Explorer is unaffected, as it bypasses this data path entirely via its own kernel driver (procexp.sys).

1. No clean-up on exit

Both effects persist even after the Claude Desktop App is closed, indicating that resources are opened but not properly released — a classic resource leak on application exit.

1. Full resolution on uninstall

Both issues disappear immediately after uninstalling the Claude Desktop App and restarting — confirming the app as the sole cause.

Error Messages/Logs

Steps to Reproduce

Here's a "Steps to Reproduce" section to replace or extend the existing one:

STEPS TO REPRODUCE

Prerequisites

Clean Windows 10 installation (Build 10.0.19041 or similar)
Firefox installed and previously used (history database exists)
No prior installation of Claude Desktop App

Setup

Download and install the Claude Desktop App from https://claude.ai/download
Launch the app and complete the initial setup / login
Do not change any default settings — reproduce with out-of-the-box configuration
Leave the app running in the background (system tray)

Reproducing Issue 1 — Task Manager crash

Press Ctrl + Shift + Esc to open the Windows Task Manager
If in compact view, click "More details" to switch to advanced view
Click on any process, column header, or tab (e.g. "Performance" or "Details")
Expected: Task Manager responds normally
Actual: Task Manager crashes immediately with APPCRASH / Access Violation (c0000005)

Reproducing Issue 2 — Firefox history lock

Close Firefox completely (ensure no Firefox process is running in Task Manager)
Launch Firefox
Expected: Firefox opens normally
Actual: Firefox displays an error stating the history database is already in use by another process (places.sqlite is locked)

Confirming the root cause

Uninstall the Claude Desktop App via Windows Settings → Apps
Restart the system
Repeat both tests above
Result: Both issues are fully resolved — confirming the Claude Desktop App as the sole cause

Reproduced on: 2 independent Windows 10 devices with identical results

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

The exact version number could not be retrieved post-uninstallation. The app was downloaded from claude.ai/download in April 2026.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_