Zen blocks local network connections with NS_ERR_CONNECTION_REFUSED

[mrkrsl]

Preliminary Checks

• I have read and understood the important section above.
• I have searched existing issues and avoided creating duplicates.
• I am not filing an enhancement request.
• I have checked that this issue cannot be reproduced on Mozilla Firefox.
• I have checked that this issue can be reproduced once I removed all my Mods and Custom CSS.

What happened?

No matter what I try, I can't connect to a service running on another machine within my local network.

The specific address is: http://192.168.1.141:3000/

Some pertinent notes:

• I can connect/load this site in standard Firefox and Chrome.
• I can ping the machine's IP address.
• I've tried without any extensions loaded.
• I've disabled, one by one, all settings in the Settings > Privacy & Security panel
• HTTPS-Only mode is set to "Don’t enable HTTPS-Only Mode", plus I added an exception anyway.
• I've also added exceptions for this domain in all relevant sections of the Settings > Privacy & Security panel
• In about:config I tried, then reverted setting privacy.globalprivacycontrol.enabled to false
• In about:config I tried, then reverted setting privacy.globalprivacycontrol.functionality.enabled to false
• In about:config I tried, then reverted setting network.http.sendSecureXSiteReferrer to true
• I added an explicit hosts file entry for the IP to a name, which resolves but still fails
• I checked the HAR logs and have been told that "Status 0 means the connection never even established - this is a network-level block, not an HTTP error"
• I tried ports 3000, 5000, 7000, 7777, 10000. All refuse to connect.
• I've tried swearing.

To be clear, this is an issue with Zen accessing another machine on the local network.

Local Zen (same machine as Docker) → ✅ Works via localhost
Remote Zen (your other machine) → ❌ Fails with status 0
Remote Chrome and Firefox (your other machine) → ✅ Works fine

It seems that there's a Zen-specific block on LAN requests, IPs or ports. All other browsers allow this site to load (no matter the port).

HAR logs below.

Expected behavior

Navigating to a legitimate LAN address (e.g. http://192.168.1.141:3000/) should load the page.

Actual behavior

Navigating to a legitimate LAN address (e.g. http://192.168.1.141:3000/) responds with Unable to connect (NS_ERR_CONNECTION_REFUSED)

Steps to reproduce

1. Open Devtools > Network panel
2. Navigate to a LAN IP address (or indeed a local server address) e.g. http://192.168.1.141:3000 where the service is confirmed to load/run in Firefox.
3. Witness the NS_ERR_CONNECTION_REFUSED error

Screenshots and videos

Zen refusing (main window) Firefox succeeding (smaller window).

Version

1.13.1b (Firefox 139.0.4) (aarch64)

What platform are you seeing the problem on?

macOS - aarch64

What component is this issue related to?

Security

Relevant log output if applicable

{
  "log": {
    "version": "1.2",
    "creator": {
      "name": "Zen",
      "version": "1.13.1b"
    },
    "browser": {
      "name": "Zen",
      "version": "1.13.1b"
    },
    "pages": [
      {
        "id": "page_3",
        "pageTimings": {
          "onContentLoad": -1750021105298,
          "onLoad": -1750021105298
        },
        "startedDateTime": "2025-06-15T21:58:25.298+01:00",
        "title": "http://192.168.1.141:3000/"
      }
    ],
    "entries": [
      {
        "startedDateTime": "2025-06-15T21:58:25.298+01:00",
        "request": {
          "bodySize": 0,
          "method": "GET",
          "url": "http://192.168.1.141:3000/",
          "httpVersion": "",
          "headers": [
            {
              "name": "Host",
              "value": "192.168.1.141:3000"
            },
            {
              "name": "User-Agent",
              "value": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:139.0) Gecko/20100101 Firefox/139.0"
            },
            {
              "name": "Accept",
              "value": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
            },
            {
              "name": "Accept-Language",
              "value": "en-GB,en;q=0.5"
            },
            {
              "name": "Accept-Encoding",
              "value": "gzip, deflate"
            },
            {
              "name": "Sec-GPC",
              "value": "1"
            },
            {
              "name": "Connection",
              "value": "keep-alive"
            },
            {
              "name": "Upgrade-Insecure-Requests",
              "value": "1"
            },
            {
              "name": "Priority",
              "value": "u=0, i"
            }
          ],
          "cookies": [],
          "queryString": [],
          "headersSize": 364
        },
        "response": {
          "status": 0,
          "statusText": "",
          "httpVersion": "",
          "headers": [],
          "cookies": [],
          "content": {
            "mimeType": "",
            "size": 0,
            "encoding": "base64",
            "text": ""
          },
          "redirectURL": "",
          "headersSize": 0,
          "bodySize": 0
        },
        "cache": {},
        "timings": {
          "blocked": 0,
          "dns": 0,
          "connect": 0,
          "ssl": 0,
          "send": 0,
          "wait": 0,
          "receive": 0
        },
        "time": 0,
        "_securityState": "insecure",
        "pageref": "page_3"
      }
    ]
  }
}

[alexanderaeppli]

I was able to replicate the issue by removing Zen's local network permissions in the system settings. Maybe have a look there? Apps that request access should automatically appear in the list. MacOS permissions are wonky at best and lead me down rabbit holes numerous times.

[mrkrsl]

I was able to replicate the issue by removing Zen's local network permissions in the system settings. Maybe have a look there? Apps that request access should automatically appear in the list. MacOS permissions are wonky at best and lead me down rabbit holes numerous times.

I thought you had it then, because Zen's Local network setting was indeed Off (and Firefox's On) when I checked. So I flipped the switch.

But ... sadly no joy. I still see the "Unable to connect" message in Zen after doing this (and also restarting Zen). Firefox still loads the page.

[alexanderaeppli]

I think its interesting that its called "Zen Browser" and not "Zen". Maybe there is a permission mix-up since the name of the app changed a couple off months ago? Though, my work MacBook has it listed as "Zen Browser" as well but the network toggle still works without restart.

Could be a lot of things. Try restarting your machine with the toggle on. After that i would suggest backing up your profile folder and reinstalling Zen.

If that does not help you might have to wait till one of the devs can take a look.