test(bidi): allow firefoxUserPrefs in Playwright's own tests

[hbenl]

Fixes the following tests in library/browsertype-connect.spec.ts:

• "run-server > socks proxy > should proxy based on the pattern"
• "run-server > socks proxy > should proxy ipv6 localhost requests"
• "run-server > socks proxy > should proxy localhost requests"

[github-actions]

Test results for "MCP"

5 failed
❌ [firefox] › mcp/cli-json.spec.ts:133 › tab-list lists all tabs @mcp-windows-latest-firefox
❌ [firefox] › mcp/cli-json.spec.ts:144 › tab-close closes a tab and returns remaining tabs @mcp-windows-latest-firefox
❌ [firefox] › mcp/cli-session.spec.ts:99 › session stops when browser exits @mcp-windows-latest-firefox
❌ [firefox] › mcp/cli-test.spec.ts:76 › debug test with custom fixture using browser.newContext @mcp-windows-latest-firefox
❌ [webkit] › mcp/config.spec.ts:138 › browser_get_config returns merged config from file, env and cli @mcp-windows-latest-webkit

6938 passed, 1052 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

2 failed
❌ [firefox-library] › library/inspector/cli-codegen-3.spec.ts:224 › cli codegen › should generate frame locators (4) @firefox-ubuntu-22.04-node20
❌ [firefox-page] › page/page-emulate-media.spec.ts:196 › should report hover and fine pointer for desktop @firefox-ubuntu-22.04-node20

3 flaky

⚠️ [installation tests] › playwright-test-package-managers.spec.ts:70 › pnpm: @playwright/test should work `@package-installations-windows-latest`
⚠️ [chromium-library] › library/video.spec.ts:682 › screencast › should capture full viewport on hidpi `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:719 › screencast › should work with video+trace `@chromium-ubuntu-22.04-node20`

41657 passed, 851 skipped

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Merge workflow run.