Firefox: Focus-sensitive Selenium tests do not work reliably in parallel test execution

This is a problem when using Selenium with Firefox. We recommend using ChromeDriver for your Selenium tests.

Firefox will not trigger focus/blur events when its window is not focused. While this makes sense in standard usage, it breaks in parallel test execution.

Please do not rely on focus events in your tests. The linked card has an example of how to build passing tests that deal with focus/blur events.