With newer macOS, Firefox can't access phpMyAdmin server, but Safari can
Please see this StackOverflow post: https://stackoverflow.com/questions/65943354/after-macos-update-client-cant-connect-to-phpmyadmin
With macOS Catalina and Big Sur, my MacBook Pro can't access phpMyAdmin on my server using Firefox. It simply acts like the server doesn't exist. Using Safari, it works normally.
Previous versions of macOS didn't appear to have this problem.