In my case, I see Exchange 2016 OWA or ECP site will not open in Firefox or Chrome or Edge browsers. In Firefox I was getting this error:
The solution for Firefox:
Open Firefox, type about:config in address bar. Search for http2, find and disable Network.http.spdy.enabled.http2. Close and reopen Firefox.
Solution, If you have access to the server:
Download and run IIS Crypto tool on the Windows Server. Click on “Best Practices” button, which chooses the protocols and chiphers as below. Reboot your server.