Playwright firefox doesn't have isolated cursor states with parallel tests

[hi-ogawa]

See #10045

Not fully sure, but the observed flaky behavior appears to indicate the issue in cursor state isolation. It can be reproduced by:

BROWSER=firefox pnpm -C test/browser/ test-fixtures --root fixtures/user-event-hover --browser.headless --fileParallelism

We should try to reproduce on playwright, then check if it's a bug or known limitation.