It's called Responsive Design Mode, and it's the third button from the the right on the top bar. Even better, use the shortcut Ctrl-Shift-M, which works even when devtools is closed.
Because you can activate mobile view in Firefox WITHOUT devtools opened, but in Chrome that's impossible.
Lot of times I hated this at Chrome.
Also, that shortcut in Firefox will immediately give you mobile view, and in Chrome not as you first need to type shortcut for Devtools.