Fix failing test: page-network-idle.spec.ts "should wait for networkidle from the popup" (Firefox)

## Test Expectation

- **Pattern:** `[page-network-idle.spec.ts] should wait for networkidle from the popup`
- **Platforms:** all (darwin, linux, win32)
- **Browsers:** Firefox only
- **Mode:** all (headless + headful)
- **Status:** FAIL

Firefox-specific failure.