This would be a great addition to the Android/iOS version(s) of Firefox and Firefox Focus, since some browsers (like Chrome/Brave) have customized QR code designs, a Firefox one could have a QR code with a fox (or other Mozilla-related icon) in the middle to show that it was made in Firefox.
A use case for Android Firefox (at least): when you're with friends and want to share a link without having to send it to them or use NFC (which nobody seems to use or know how to use). With the diversity of devices and messaging platforms (FB messenger, imessage, signal, email, SMS ๐คฎ), a QR code is way easier.
Which is probably why restaurants use QR codes๐คทโโ๏ธ