When I open a project, the code isn't appearing. I use Firefox version 67.0.4 (64-bit). Is it just that repl.it doesn't support Firefox? Or is something wrong with my browser.
I use the same version of FF and the code is appearing fine. Try refreshing the page, or logging out of repl.it, closing the browser, opening it and logging in again. If that does not work reboot your computer and login to repl.it again.