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.
https://github.com/substack/minimist/blob/aeb3e27dae0412de5c0494e9563a5f10c82cc7a9/index.js

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?