Firefox shows forward-logs-shared.ts as source in console for all next logs

[kriskratz]

Link to the code that reproduces this issue

https://github.com/kriskratz/nextjs-console-log

To Reproduce

1. Start the application (next dev), note: code is a fresh install of Next v16.1.1
2. Open application in Firefox
3. Click anywhere on page to generate log
4. View logs in DevTools > Console

Current vs. Expected behavior

Firefox console logs all show "forward-logs-shared.ts" as source, but it should show "page.tsx" as the source.

Started with Next v16.

Chrome logs correctly show "page.tsx" as the source.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.6.0: Wed Oct 15 21:12:15 PDT 2025; root:xnu-11417.140.69.703.14~1/RELEASE_ARM64_T6041
  Available memory (MB): 65536
  Available CPU cores: 16
Binaries:
  Node: 24.11.0
  npm: 11.6.2
  Yarn: 1.22.22
  pnpm: 9.9.0
Relevant Packages:
  next: 16.1.1 // Latest available version is detected (16.1.1).
  eslint-config-next: N/A
  react: 19.2.3
  react-dom: 19.2.3
  typescript: 5.9.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Not sure

Which stage(s) are affected? (Select all that apply)

next dev (local)

Additional context

I tested the code on a fresh install of Next with a clean install of Firefox.

[aldoprogrammer]

Hi, I’d like to work on this issue. I can reproduce it in Firefox, Chrome and Edge, and I’ll submit a fix to make the console log show the correct source (page.tsx)

[aldoprogrammer]

I was able to reproduce this in Firefox, Chrome, and Edge.

After investigation, this appears to be expected behavior when
experimental.browserDebugInfoInTerminal or experimental.mcpServer is enabled.

Console methods are intentionally wrapped and forwarded via forward-logs-shared.ts.
Chromium-based browsers can still resolve the original callsites via source maps,
but Firefox currently does not, so it shows forward-logs-shared.ts as the source.

Disabling terminal / MCP logging restores original callsites in Firefox.

Unless the logging design changes or Firefox improves source map resolution,
this behavior seems expected.

[kriskratz]

Thanks for getting back to me so quickly.

I added this to the example project's next.config.ts:

  experimental: {
    browserDebugInfoInTerminal: false,
    mcpServer: false,
  }

It's not working for me in Firefox. Is there something else I'm missing or is it like you said, expected behavior?

It's extra frustrating because callsites worked until I upgraded to Next v16, and DevTools are far more responsive in Firefox.

[fantactuka]

This one causing few DX issues:

• Can't find where log is initiated (especially when it's third party library)
• Can't filter out specific logs (e.g., hiding logs from trpc lib to reduce verbosity in dev mode during debuging)

Both used to be one click in dev tools