On macOS Safari Version 11.1.2 (13605.3.8), I can scroll horizontally (it's cute, I can see all the flags coming) and I can't really search the website. I put in values, hit return, and nothing happens. Works amazingly on Chrome.
My sever has just been upgraded. Can you confirm if you're still having issues or not?
Pressing enter with either textfield selected doesn't do anything on Safari.
Firefox and Chrome work perfectly fine.
EDIT: I didn't dig deep, but changing the "marquee" width from 3000px to 100vw, fixed it, but made the flags slower.