server cannot be found

Desktop iMac running Sonoma 14.2.1 cannot connect to the server. After downloading the new version of Firefox I turned off the computer. Next time I turned it on it couldn't connect to the server. It's not just Firefox, it's Safari and anything else that depends on the server, such as cloud back-up. However, an old computer I've kept but seldom use can connect to the server. Laptop and phone connect to server. There's one server. I can access the iMac through screen sharing using the laptop. Some setting apparently got changed by Firefox. Or Firefox had nothing to do with it.

I've gone through system settings but don't know what to look for or where. I've turned the computer off and back on multiple times. Any advice? Do I really need to take the computer in for repair?