PabloSLR Ideal for me would be clicking the same button again to close it. Feels most intuitive. A button marked X like the other pop up menu's would be good as well.
It would even be better if menu's that pop up and buttons that lead you to a new adress would have a clear difference. Currently the bottom bar has all buttons that link to other places on the site aside from that single menu button while they look identical.
Anything to make a clear distinguish will be good and personally I would love to see my library listed with the rest of the menu's similar to when you are in vr. It feels kinda odd to have a separate place in the browser on mobile while on browser pc and in vr its on the left with the rest of the menus.
Hope this gives some insight.