[Browser Mode]: flaky firefox `Failed to connect to the browser session`

[OrbisK]

Describe the bug

We have some flaky failed tests with this error:

✓  browser (firefox)  vitest-example/1.test.ts (2 tests) 68ms
⎯⎯⎯⎯⎯⎯ Unhandled Errors ⎯⎯⎯⎯⎯⎯

Vitest caught 1 unhandled error during the test run.
This might cause false positive tests. Resolve unhandled errors to make sure your tests are not affected.

⎯⎯⎯⎯⎯⎯ Unhandled Error ⎯⎯⎯⎯⎯⎯⎯
Error: Failed to connect to the browser session "5086ef5f-269b-4141-886f-baee9a1f02db" within the timeout.
 ❯ Timeout._onTimeout node_modules/.pnpm/vitest@3.0.4_@types+node@22.12.0_@vitest+browser@3.0.4/node_modules/vitest/dist/chunks/cli-api.Ci-9Ccnz.js:5078:20
 ❯ listOnTimeout node:internal/timers:594:17
 ❯ process.processTimers node:internal/timers:529:7


Error: Process completed with exit code 1.

Maybe this is just a plain playwright issue, but i am not sure how to debug this.

Reproduction

https://github.com/OrbisK/vitest-playwright-firefox-reprodudction

1. fork repo
2. dispatch Example workflow
3. ca 10% of tests should fail

https://github.com/vueuse/vueuse

System Info

System:
    OS: Linux 6.8 Ubuntu 24.04.1 LTS 24.04.1 LTS (Noble Numbat)
    CPU: (8) x64 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz
    Memory: 49.16 GB / 62.58 GB
    Container: Yes
    Shell: 5.9 - /usr/bin/zsh
  Binaries:
    Node: 23.5.0 - ~/.nvm/versions/node/v23.5.0/bin/node
    npm: 10.9.2 - ~/.nvm/versions/node/v23.5.0/bin/npm
    pnpm: 8.15.9 - ~/.nvm/versions/node/v23.5.0/bin/pnpm
    bun: 1.1.42 - ~/.nvm/versions/node/v23.5.0/bin/bun
  Browsers:
    Chrome: 130.0.6723.69
  npmPackages:
    @vitejs/plugin-vue: ^5.2.1 => 5.2.1 
    @vitest/browser: ^3.0.4 => 3.0.4 
    playwright: ^1.50.0 => 1.50.0 
    vitest: ^3.0.4 => 3.0.4 
    vitest-browser-vue: ^0.1.0 => 0.1.0 

Used Package Manager

pnpm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[OrbisK]

Downgrading playwright to 1.49.0 does work. https://github.com/OrbisK/vitest-playwright-firefox-reprodudction/tree/refs/heads/downgrade/playwright

[OrbisK]

Failing with 1.50.1 too

[OrbisK]

happening for 1.49.0 too: https://github.com/vueuse/vueuse/actions/runs/13281724853/job/37081378058

[sheremet-va]

Seems like we've also been getting these errors in Vitest monorepo tests

[OrbisK]

happening for 1.49.0 too: https://github.com/vueuse/vueuse/actions/runs/13281724853/job/37081378058

If it helps: 1.49.0 works fine with node >18, but is flaky with node 18

EDIT: okay, is still flaky with >18. but better 😅

[odzhychko]

It might be related to microsoft/playwright#34586

[kigawas]

Only see this on ubuntu and windows

[BePo65]

I have the same effect using the esday library (see issue #51 of esday). I can reproduce the problem on my local windows machine. The issue of playwright that @odzhychko cited sound plausible to me.

Perhaps it helps tracking down the cause of this problem by using my minimal project esday-ViTest-Error.
That project shows the effect when run locally on windows (unluckily the github action does not show the effect and I did not yet have the time to look at that point).

Using playwright@~1.49 "solves" the problem).