A few suggestions --

Either ignore the message about 'favicon.ico', or touch that file in your root directory -- it's a web browser trying to request a 'Favorites Icon', so it'll show a little 16x16 image in your location bar. Any internet search for 'favicon.ico' should bring up some info on how to create one, if you want to go that route.

By your comment 'my code is saved as a unix file', I'm going to assume that it wasn't created on a unix system, or that you're using an editor like BBEdit that makes a distinction on what line endings and/or content encoding it uses. Whatever the case, change the shebang line to include '--' as it'll reduce the chance of DOS line endings from screwing up your files.

And, make sure you've set the proper permissions on the file:

chmod o+rx /Library/WebServer/CGI-Executables/first.pl