You're a web developer. You use a retina display. You want to see what your site looks like on a 1x display.
Run Blind concurrently with your normal browser to see what your site looks like in 1x resolution.
Safari has a 'low-resolution mode,' but it doesn't accurately represent what a 1x resolution display looks like.
Get comfortable with how your clients and others will view your work. Get Blind today from the Mac App Store.