Your browser is out of date! Update your browser to view this website correctly. Browser and Windows fully updated, both chrome and edge dont work, firefox does. edge and firefox no extension installed

“Your browser is out of date! Update your browser to view this website correctly.”

Browsers and Windows fully updated, both chrome and edge dont work, firefox does. edge and firefox no extension installed. Started happening after setting WAF rule

What is the domain?

art4u .pt

only happens when logging in to admin

Have you checked for unexpected redirect rules and other indicators of compromise?