Not affiliated with the site at all, but just confirmed in Vivaldi that https://httpstat.us/108 returns a 500 "This page isn't working" error, while Firefox just shows a blank page (and a 500 error in the Network inspection tab). Even get a 500 error with wget ("GNU Wget 1.16 built on linux-gnueabihf.")
Looked through the source briefly but couldn't understand exactly how it's working, so I'm not sure yet if it's more likely an issue on the server or "browser"...
Looking into it further, they seem to be using Kestral web server on an azure app service. I assume the server doesn't like serving those status codes for some (understandable) reason. My first guess was that it was some reverse proxy causing the problem.
Looked through the source briefly but couldn't understand exactly how it's working, so I'm not sure yet if it's more likely an issue on the server or "browser"...