[Bug]: locale is not propagated to workers in firefox

[Skn0tt]

Version

95a728a

Steps to reproduce

playwright/tests/library/browsercontext-locale.spec.ts

Line 166 in 95a728a

it('should format number in workers', async ({ browser, server }) => {

This test passes in CI, but not locally. I assume it's because CI locale happens to give the same output as es-MX. If you change the locale to ru-RU, it should also fail in CI.

It seems that workers are not respecting the context locale.

Expected behavior

Workers should be respecting context locale.

Actual behavior

Workers are using system locale.

Additional context

found during microsoft/playwright-python#3026

Environment

System:
    OS: macOS 26.2
    CPU: (12) arm64 Apple M3 Pro
    Memory: 133.67 MB / 18.00 GB
  Binaries:
    Node: 20.19.0 - /Users/skn0tt/.local/state/fnm_multishells/66603_1769161758461/bin/node
    Yarn: 1.22.22 - /Users/skn0tt/.local/state/fnm_multishells/66603_1769161758461/bin/yarn
    npm: 9.9.4 - /Users/skn0tt/.local/state/fnm_multishells/66603_1769161758461/bin/npm
    pnpm: 10.28.1 - /Users/skn0tt/.local/state/fnm_multishells/66603_1769161758461/bin/pnpm
    Deno: 2.5.2 - /opt/homebrew/bin/deno
  IDEs:
    VSCode: 1.108.1 - /opt/homebrew/bin/code
    Claude Code: 2.1.15 - /opt/homebrew/bin/claude
  Languages:
    Bash: 3.2.57 - /bin/bash

[Skn0tt]

@aslushnikov could you take a look? this seems to have regressed in the last roll.