Problems debugging a barebones create-react-app

I'm trying to debug a barebones create-react-app and I'm a little bit confused by the instructions on how to setup vscode-firefox-debug. Below is my launch configuration:
```
{
"name": "Launch Firefox",
"type": "firefox",
"request": "launch",
"reAttach": true,
"url": "http://localhost:3000/index.html",
"webRoot": "${workspaceFolder}"
}
```
First, just launching my app from vscode is not enough for me to be able to debug it: it doesn't launch the app at all. I had to start the app from the terminal and then launch this configuration for vscode to start debugging the app, is that how it's supposed to be done? The Chrome debugger documentation makes this explicit but I'm not sure if that is the case for the Firefox debugger as well. Second, the launch configuration included in the documentation didn't work before I added the port number to the `url` field, was it supposed to work without it? Not sure if something is just fundamentally wrong in my setup or if it's working like it's supposed to now. Any help or pointers to further documentation to read would be appreciated.