How to show this pop again?

I opened the page for the first time and saw it.
I drew a red box for the pop-up window in the picture.

But the pop window never show again after i closed it.
what is it?

Hi @efilw,

I have to admit, I’m unfamiliar with that pop-up window. It might be part of some A/B testing for a new feature. Do you have any browser plugins or extensions that interact with GitHub?