Wrong URL

localhost://3000 is wrong, it should be http://localhost:3000

Auto launch

If you're trying to get Create React App to open the dev page automatically, you may need to set your browser explicitly. Look at the environment variable called BROWSER in the Create React App config. It will look like this BROWSER=chrome, and you can put this in the .env file at the root of your directory. chrome might not be the right value, check documentation.

If the browser doesn't automatically launch, there may be an issue with your OS

concerning the execution of an application developed with react js if I type npm start; the execution does not start automatically; the terminal shows me the url that I must type and I write it manually in my browser. and I notice that a similar problem occurs when I type herroku login if I want to deploy a project. I think there is a problem with my browser