ua

gsettings set org.gnome.Epiphany user-agent "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.79 Safari/537.36 Edge/14.14393"

GNOME Web:

Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/604.1 (KHTML, like Gecko) Version/11.0 Safari/604.1 Epiphany/3.24.2

Apple Safari:

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_2) AppleWebKit/601.3.9 (KHTML, like Gecko) Version/9.0.2 Safari/601.3.9