When cursor-ide-browser is unavailable (MCP server "cursor-ide-browser" not found), the agent falls back to shell open https://…, which launches/focuses the system browser (Brave) instead of staying inside Cursor’s Browser Tab. User-observed feel of “taking over” a Brave tab. Agent verified system open + Glass open_resource; not CDP attach to Brave.
Steps to Reproduce
Reproduce missing cursor-ide-browser (cold-start not found or after MCP lease drop)
Ask agent to open a URL in the browser
Observe agent uses open <url> (or equivalent) → Brave comes to foreground
Optionally later open_resource opens Glass Browser Tab separately
Expected Behavior
If Browser Automation is On (Browser Tab), agent should only target Cursor Browser Tab and should not fall back to system open/Brave. If MCP is missing, agent should report failure rather than hijacking the user’s system browser.
Operating System
MacOS
Version Information
IDE:
Version: 3.13.21
Commit: 55434bd8062ece6fee083b82beed2aee42d253f0
OS: Darwin arm64 25.5.0
Brave is system browser.
For AI issues: which model did you use?
Cursor Grok 4.5
For AI issues: add Request ID with privacy disabled
N/A — failure is MCP routing / Browser Automation wiring, not a model completion error.
Data sharing on. When cursor-ide-browser is missing from agent MCP runtime, the agent fell back to shell open → system Brave focused (not CDP into Brave). Attaching the session package so support can correlate.
Correlation for this report
Failure mode in agent: MCP server "cursor-ide-browser" not found
Concurrent catalog: empty-window writer still shows toolCount=16 + leave-the-lease churn (see 01-* attachments)
RequestIds from the project chat window (wb62): ea519e6d-beca-48ec-a1cc-0f2014441f94, 39c62806-5a07-4e7b-a817-a2f6b664a5c8
composerId: 5acf3d63-e855-475f-80d3-765ec4494774
Session / identity (data sharing on)
machineId:45f9fb3f-e7a9-4793-a235-3a7bb93e4e3f
Cursor: 3.13.21 (55434bd8062ece6fee083b82beed2aee42d253f0) Darwin arm64
We’ve seen this reported before, and I’ve flagged your case for our team. Two things line up with what you’re describing:
When cursor-ide-browser is unavailable, the shared prompt component that tells the agent “don’t use the shell to interact with the browser” is gated on the browser tools being present - so it disappears with the MCP, and the agent falls back to open <url>.
When Cursor is handed an HTTP(S) URL to open, the choice between the built-in Cursor Browser Tab and the OS opener currently only checks the “open web links in browser” preference. Your Browser Tab preference (lastBrowserConnectionMode) isn’t consulted on that path, which is why “Cursor Browser Tab” doesn’t kick in.
You’re already doing the right things - the workaround in this related thread helps if the underlying churn is what’s making the MCP unavailable in the first place. Two more things you can try in the meantime:
Turn on “Open web links in the Cursor browser” in Cursor Settings → Browser. That won’t stop the agent from running open <url> in the terminal (that’s the bug), but it’ll make any URL Cursor itself hands to the OS route into the Cursor Browser Tab instead of Brave, which reduces context switching.
Add a User Rule along the lines of: “When you need to open a URL, use the cursor-ide-browserbrowser_navigate tool. Never run open <url> in the shell to open a web page.” This gets the same guidance in front of the agent even when the browser tools aren’t attached to the session.