The browser is Orion, built by Kagi.

On first try it felt like it was taking inspiration from Arc. It's even got the hotkey for copying URLs like Arc (which I use all the time) and the sidebar tabs option. But, unlike Arc, which ships with Zaps and Chrome Extension support, Orion ships with a certain Chrome Extension pre-installed: VisBug!

I always wanted a browser to ship with tools for designers! This is rad!

Here's a preview of what it's like in Orion to use the "Design Tools":

Thanks for the tip Kilian!