My apologies. I found where this feature is: 

1) Click far upper right chevron icon  (<<)

2) Click toggle the resize tooltip icon ( i )

Hello and thank you for your work on this extension!

I would love to see the current window/viewport height and width values independently of the preset selection. In the situation where I resize my browser manually with my cursor and want to know my current window size, can the "(current)" values be presented as integers along with or replacing the "(current)" text?